Showing posts with label grading. Show all posts
Showing posts with label grading. Show all posts
Friday, April 27, 2012
Understanding technology Post-harvesting
When it comes to processing perishable crops, what is done to the crops the moment they are uprooted from the ground determines the final quality of the said crop, to a very large extent. As the name suggests, the act of processing the crop ( Dusting, sorting, cleaning and packing the crops) after the harvest, is called Post harvesting. It becomes a critical part in processing perishable food crops because these crops have a tendency to deteriorate from the moment they are uprooted from the farms. Processed food items, fresh farm produce or whatever it is that the crop ought to be sold for, the out put of the post harvesting technology largely determines the caliber of the processed food crop.
Though it might seem like an obvious thing to do post harvesting the crop, it is still a difficult task to be achieved either due to lack of awareness or due to the lack of infrastructure. Post harvest usually consists of cleaning up of the crops, removing moisture and bringing down the pace of the chemical reactions that usually occur then. These chemical reactions can also occur, in some cases, when two crops are stored together, given a particular temperature. To avoid this and also to streamline the post harvesting operations a lot of expensive equipment has to be put in place like complicated sorting, packing, storing and facilities for moving perishable crops about in storage areas are duly put in place, more so,if we are talking about a fully functional industrial size which comes equipped with conveyor belts for moving these crops around, cold-storage facilities,atmosphere-controllable storage equipment and advanced sorting and harvesting machinery.
The above mentioned sophisticated equipment, coupled with state-of-the-art technology managed efficiently with superbly trained staff should be able to battle with the time constrained challenge of being able to produce the best quality output, especially with regards to the perishable food crops and hence becomes an important element in the food processing chain.
Be it your home garden which delivers some kind of perishables or an industrial unit, a few things have to be considered carefully and attended to. Firstly, the crops need to be culled (removal of damaged crop elements). Secondly, the perishables need to be cooled immediately and maintained at that temperature to avoid further possible degradation of crops and finally, the crops have to be handled expertly and with care.
Saturday, February 18, 2012
POSTHARVEST HANDLING OF CITRUS
FRUIT MATURITY AT HARVEST
In tropical and subtropical countries, the development of the fruit is affected by the temperature. Maturity of the rind and maturity of the flesh of the fruit are not synchronized. The fruit is edible even when the rind still remains green .
Mature fruit vary in size, even those on the same tree With sweet oranges such as Valencia or Liucheng, harvesting should begin with the smaller fruit which mature first.
With mandarins such as Ponkan, it is the end of the fruit furthest from the stem which turns yellow first. Harvesting should begin with the large fruit. Smaller fruit, or those which are slow to turn color, should be harvested later on in the season.
TIME OF DAY FOR HARVEST
It is best to harvest citrus on a clear, sunny day with low humidity. The fruit should be harvested as soon as the dew has evaporated. On a cloudy day, the fruit should be harvested in the afternoon. Fruit should not be harvested at all on a rainy day.
HARVESTING METHOD
To prevent physical damage to the fruit, the worker should trim his/her fingernails, wear gloves, and use special harvesting scissors with rounded ends to cut the fruit. To harvest the fruit, it should be held in one hand, and the other hand used to cut the fruit stem together with a few leaves . Then the fruit is brought close to the chest and the rest of the stem is cut off smoothly, close to the fruit .
CONTAINERS USED FOR HARVESTING
The container used for newly harvested fruit should be solid, with good ventilation Fruit in flexible containers tend to crush each other, causing bruises. The bottom of wood or bamboo containers should be lined with newspapers, a paper bag or a fertilizer sack. It is important to move containers as little as possible, and not to leave them standing in the sun
GRADING AND STORABILITY
Citrus are graded by size. This can be done by hand or by machine. If the grower is grading citrus manually, it is best not to judge the size only by eye, but to use some kind of measuring device. A simple way to check fruit size is to cut a series of round holes in a thin wooden board or a piece of thick cardboard, according to standard market sizes for that variety (Fig. 6). A revolving drum type machine is often used by farmers in Taiwan. Other low-cost grading machines are also available.
Fruit of different sizes should not be mixed together, or the market price the grower gets may be only that of the smallest fruit.
The optimum size for fruit varies from one variety to another. Generally, large fruit fetch the highest price. However, in the case of mandarins such as Ponkan, large fruit (8.5 cm in diameter) and extra large fruit (9.0 cm in diameter) have a low level of total soluble solids and low acid content. They have a thick peel and little juice, and do not store well. They should be consumed soon after harvest.
Medium sized (8.0 cm in diameter) and small-sized (7.5 cm in diameter) Ponkan fruit have a higher level of total soluble solids and a higher acid content, so that the flavor improves after short-term storage.
In the case of oranges such as Valencia and Liucheng, the total soluble solids and acid content fall as fruit become larger. Small fruit (6.0 - 6.5 cm in diameter) have a thin rind and high total soluble sugars and acid, but also are more likely to rot in storage. They should be consumed fresh. Medium sized fruit (7.0 - 7.5 cm in diameter) have a low incidence of fruit rot after storage. Tests have shown they still have a good flavor after two months of storage. Large fruit (more than 7.5 cm in diameter) have a low incidence of fruit rot but a poor flavor after storage, because of their low level of total soluble sugars and their low acid content.
TREATMENT AFTER HARVEST
Only fruit which have not been damaged in harvest are used for storage, although it is difficult to harvest fruit without some minor damage. Sometimes a chemical treatment is applied to the fruit before storage, to reduce the incidence of postharvest diseases.
Citrus fruit age during storage. The stem becomes first yellow, then brown. Finally, it drops off, leaving a vulnerable place on the fruit which may be infected by fungus diseases. A treatment of 10 to 40 ppm 2,4-D can prevent the fruit stem from drying up and dropping off.
The chemical thiabendazole (40% diluted at 500X) can be sprayed onto fruit one or two weeks before harvest. Alternatively, fruit can be soaked for three minutes immediately after harvest. The treatment reduces the incidence of fruit rot during storage. Iminoctodine 25%, (diluted at 2000X) can be used as a spray four days before harvest, or used to soak the fruit before they are packed. It also reduces the incidence of fruit rot.
OTHER TREATMENTS BEFORE STORAGE
After harvest or chemical treatment, fruit should be kept in the shade for a few days before they are put into a PE plastic bag. The bag should be 0.02 - 0.03 mm thick. Keeping the fruit in the shade in this way is a curing treatment, to reduce the water content of the peel. This reduces cell activity in the peel, which otherwise might soften the fruit.
The time needed for water loss or evaporation depends on the temperature, the length of time the fruit is to be stored, and the thickness of the peel. If temperatures are high, citrus fruit need a longer period of curing. They also need a longer period of curing if they are to be stored for a long time, or if they have a thick peel.
On average, it takes from three to seven days to reduce the fruit weight by about 3%. A higher water content than this causes to condense inside the plastic bag, leading to stem rot. Water loss may cure minor wounds on the peel and reduce the incidence of rot during storage.
Fruit which are to be stored for a long period are wrapped in plastic, to reduce water loss. Sometimes only one fruit is kept in each bag. This is the case with mandarins such as Ponkan. However with other varieties such as Valencia or Tonkan, several layers of fruit can be stored in each bag.
If the fruit are to be stored for more than two months, PE film is used, wrapped around stacked crates of fruit to form a pillar.
STORAGE
Plastic crates or boxes are used for storing fruit. Mandarins such as Ponkan should be stored with only one or two layers per box. Sweet oranges such as Valencia or Liucheng should be stored with three or four layers per box. Too many layers in one box may cause bruising of the fruit.
Boxes should be stacked inside the storage room in a way that maintains good ventilation. For the first few weeks of storage, ventilation windows should be left open. Throughout the storage period, the windows should be left open at night or in cold weather, in order to cool the fruit.
When temperatures are high in the day time, the ventilation windows should be closed. Sunlight should not be able to penetrate inside the storage room. Any rotting fruit that are found should be removed.
Storage rooms should be constructed in places where cold air can flow into the room at night. The storage room should have a high roof, to allow better circulation of cold air at night. Ventilation windows should be small but there should be a large number of them, to allow better air circulation. It is recommended to that some ventilation pipes should be buried under ground, to bring in cool air through the floor of the room.
The roof and walls should have good heat insulation, to keep temperatures as cool as possible. The storage room should be insect-proof and rat-proof. A good storage room is the key for extending the shelf life while maintaining fruit quality. The room should be kept clean, and all rotting fruits should be removed. Before storage, the room should be sanitized by washing the walls and floor with 5% formalin.
Another way of storing fruit is to leave them on the tree. In California, Valencia oranges can be left on the tree for five months, from May to October. In Taiwan, this has been tried for the very similar Liucheng orange. However, the harvest can only be delayed for one month and then the fruit drop to the ground.
In tropical and subtropical countries, the development of the fruit is affected by the temperature. Maturity of the rind and maturity of the flesh of the fruit are not synchronized. The fruit is edible even when the rind still remains green .
Mature fruit vary in size, even those on the same tree With sweet oranges such as Valencia or Liucheng, harvesting should begin with the smaller fruit which mature first.
With mandarins such as Ponkan, it is the end of the fruit furthest from the stem which turns yellow first. Harvesting should begin with the large fruit. Smaller fruit, or those which are slow to turn color, should be harvested later on in the season.
TIME OF DAY FOR HARVEST
It is best to harvest citrus on a clear, sunny day with low humidity. The fruit should be harvested as soon as the dew has evaporated. On a cloudy day, the fruit should be harvested in the afternoon. Fruit should not be harvested at all on a rainy day.
HARVESTING METHOD
To prevent physical damage to the fruit, the worker should trim his/her fingernails, wear gloves, and use special harvesting scissors with rounded ends to cut the fruit. To harvest the fruit, it should be held in one hand, and the other hand used to cut the fruit stem together with a few leaves . Then the fruit is brought close to the chest and the rest of the stem is cut off smoothly, close to the fruit .
CONTAINERS USED FOR HARVESTING
The container used for newly harvested fruit should be solid, with good ventilation Fruit in flexible containers tend to crush each other, causing bruises. The bottom of wood or bamboo containers should be lined with newspapers, a paper bag or a fertilizer sack. It is important to move containers as little as possible, and not to leave them standing in the sun
GRADING AND STORABILITY
Citrus are graded by size. This can be done by hand or by machine. If the grower is grading citrus manually, it is best not to judge the size only by eye, but to use some kind of measuring device. A simple way to check fruit size is to cut a series of round holes in a thin wooden board or a piece of thick cardboard, according to standard market sizes for that variety (Fig. 6). A revolving drum type machine is often used by farmers in Taiwan. Other low-cost grading machines are also available.
Fruit of different sizes should not be mixed together, or the market price the grower gets may be only that of the smallest fruit.
The optimum size for fruit varies from one variety to another. Generally, large fruit fetch the highest price. However, in the case of mandarins such as Ponkan, large fruit (8.5 cm in diameter) and extra large fruit (9.0 cm in diameter) have a low level of total soluble solids and low acid content. They have a thick peel and little juice, and do not store well. They should be consumed soon after harvest.
Medium sized (8.0 cm in diameter) and small-sized (7.5 cm in diameter) Ponkan fruit have a higher level of total soluble solids and a higher acid content, so that the flavor improves after short-term storage.
In the case of oranges such as Valencia and Liucheng, the total soluble solids and acid content fall as fruit become larger. Small fruit (6.0 - 6.5 cm in diameter) have a thin rind and high total soluble sugars and acid, but also are more likely to rot in storage. They should be consumed fresh. Medium sized fruit (7.0 - 7.5 cm in diameter) have a low incidence of fruit rot after storage. Tests have shown they still have a good flavor after two months of storage. Large fruit (more than 7.5 cm in diameter) have a low incidence of fruit rot but a poor flavor after storage, because of their low level of total soluble sugars and their low acid content.
TREATMENT AFTER HARVEST
Only fruit which have not been damaged in harvest are used for storage, although it is difficult to harvest fruit without some minor damage. Sometimes a chemical treatment is applied to the fruit before storage, to reduce the incidence of postharvest diseases.
Citrus fruit age during storage. The stem becomes first yellow, then brown. Finally, it drops off, leaving a vulnerable place on the fruit which may be infected by fungus diseases. A treatment of 10 to 40 ppm 2,4-D can prevent the fruit stem from drying up and dropping off.
The chemical thiabendazole (40% diluted at 500X) can be sprayed onto fruit one or two weeks before harvest. Alternatively, fruit can be soaked for three minutes immediately after harvest. The treatment reduces the incidence of fruit rot during storage. Iminoctodine 25%, (diluted at 2000X) can be used as a spray four days before harvest, or used to soak the fruit before they are packed. It also reduces the incidence of fruit rot.
OTHER TREATMENTS BEFORE STORAGE
After harvest or chemical treatment, fruit should be kept in the shade for a few days before they are put into a PE plastic bag. The bag should be 0.02 - 0.03 mm thick. Keeping the fruit in the shade in this way is a curing treatment, to reduce the water content of the peel. This reduces cell activity in the peel, which otherwise might soften the fruit.
The time needed for water loss or evaporation depends on the temperature, the length of time the fruit is to be stored, and the thickness of the peel. If temperatures are high, citrus fruit need a longer period of curing. They also need a longer period of curing if they are to be stored for a long time, or if they have a thick peel.
On average, it takes from three to seven days to reduce the fruit weight by about 3%. A higher water content than this causes to condense inside the plastic bag, leading to stem rot. Water loss may cure minor wounds on the peel and reduce the incidence of rot during storage.
Fruit which are to be stored for a long period are wrapped in plastic, to reduce water loss. Sometimes only one fruit is kept in each bag. This is the case with mandarins such as Ponkan. However with other varieties such as Valencia or Tonkan, several layers of fruit can be stored in each bag.
If the fruit are to be stored for more than two months, PE film is used, wrapped around stacked crates of fruit to form a pillar.
STORAGE
Plastic crates or boxes are used for storing fruit. Mandarins such as Ponkan should be stored with only one or two layers per box. Sweet oranges such as Valencia or Liucheng should be stored with three or four layers per box. Too many layers in one box may cause bruising of the fruit.
Boxes should be stacked inside the storage room in a way that maintains good ventilation. For the first few weeks of storage, ventilation windows should be left open. Throughout the storage period, the windows should be left open at night or in cold weather, in order to cool the fruit.
When temperatures are high in the day time, the ventilation windows should be closed. Sunlight should not be able to penetrate inside the storage room. Any rotting fruit that are found should be removed.
Storage rooms should be constructed in places where cold air can flow into the room at night. The storage room should have a high roof, to allow better circulation of cold air at night. Ventilation windows should be small but there should be a large number of them, to allow better air circulation. It is recommended to that some ventilation pipes should be buried under ground, to bring in cool air through the floor of the room.
The roof and walls should have good heat insulation, to keep temperatures as cool as possible. The storage room should be insect-proof and rat-proof. A good storage room is the key for extending the shelf life while maintaining fruit quality. The room should be kept clean, and all rotting fruits should be removed. Before storage, the room should be sanitized by washing the walls and floor with 5% formalin.
Another way of storing fruit is to leave them on the tree. In California, Valencia oranges can be left on the tree for five months, from May to October. In Taiwan, this has been tried for the very similar Liucheng orange. However, the harvest can only be delayed for one month and then the fruit drop to the ground.
Friday, February 17, 2012
POST HARVEST MANAGEMENT
Curing
The only post-harvest treatment required for the long storage of bulb onions is a thorough curing of the bulbs. Curing is a drying process intended to dry off the necks and outer scale leaves of the bulbs to prevent the loss of moisture and the attack by decay during storage. The essentials for curing are heat and good ventilation, preferably with low humidity. This dries out the neck and the two or three outer layers of the bulb. The outermost layer, which may be contaminated with soil, usually falls away easily when the bulbs are cured, exposing the dry under-layer, which should have an attractive appearance. Onions are considered cured when neck is tight and the outerscales are dried until they rustle. This condition is reached when onions have lost 3 to 5% of their weight.
If onions cannot be dried in the field, they can be collected in trays, which are then stacked in a warm, covered area with good ventilation.
In cool, damp climates, onions in bulk ventilated stores are dried with artificial heat blown through the bulk at a duct temperature of 30 degrees Celsius.
Onions can also be cured by tying the tops of the bulbs in bunches and hanging them on a horizontal pole in a well-ventilated shades. Curing in shade improves bulb colour and reduces losses significantly during storage
Grading
Onions after curing are graded manually before they go in to storage or for marketing. The thick neck, bolted, doubles, injured and decayed bulbs are picked out so also misshapen small bulbs. Sorting and grading is done after storage also to fetch better price. The outer dry scales usually rub off during the grading process, giving the onions a better appearance for market. It has been experienced that if storage is arranged after proper sorting and grading losses in storage are reduced.
For local market the onions are graded based on their size.
Extra large onion (>6 cm dia.)
Medium (4-6 cm dia.)
Small (2-4 cm dia.)
The extra large onions have great demand and fetches very good price.
General Characteristics
The bulbs shall:
• be reasonably uniform in shape, size colour and pungency of the variety /type
• be mature, solid in feel, reasonably firm with tough clinging skins.
• be throughout cured and dried.
• be free from dust and other foreign material.
• be free from defective, diseased, decayed and damaged bulbs caused by seed stems, tops
• oots, moisture, dry sun scald burn, sprouting, mechanical or other injuries and staining.
• be free from moulds, soft rot and insect attack.
• % of seed stem or bolted bulbs shall not exceed 20% in Nasik kharif onions.
Bangalore and Krishnapuram onions will be free from bottle necks or doubles.
Grade designations and definitions of quality for export of onions:
Different size but not below 15
1. Tolerance for size in big onions: For accidental errors in sizing, not more than 5 % by weight of the bulbs in any lot may be of next lower grade than the minimum diameter prescribed in Nasik, Saurashtra, Bellary or Poona onions. In case of Podisu, this error in sizing not more than 10 % by weight. In this case, smallest onion in bunch would be taken for measuring the diameter.
2. Defective, diseased and damaged shall mean malformed bulbs and the bulbs internally or externally damaged, diseased or discoloured material affecting the quality. The decayed onions shall not exceed 2% in any lot.
General: The grade shall be allowed to be packed only against irrevocable letter of credit.
# NS grade: This is not a grade in its strict sense but has been provided for the onions not covered under regular grade. Onions under this grade shall be exported only against a specific order from foreign buyer inducting the quality.
Packaging
Packing should be small for easy handling during transit and may vary according to market demand. Onions are packed in jute (hessian) bags for transporting to yard or brought as loose. For safe handling, 40 kg open mesh jute bags having 200-300 g weight should be used in domestic market. For export, common big onions are packed in 5-25 kg size open mesh jute bags.
Bangalore Rose and multiplier onions are packed for export in 14-15 kg wooden baskets. Nylon net bags, when used for packing have resulted in less storage loss because of good ventilation.
Handling
Bulbs intended for storage must be free from cuts and handled with extreme care. Onions should not be dropped on to non-resilient surface from more than 6 feet height. If onions are to be stacked after packing in store or trucks, the better height is 2-2.5 metres. Losses due to rot is reported to be more if onions are stored in gunny bags than in loose or wooden crates.
Storage
Proper storage of bulbs is necessary both for consumption and also for seed production. Onions should not be stored unless adequately dried either in the field or by artificial means. It is necessary to dry the neck tissue and outer scales until they rustle when handled otherwise the bulbs will rot in storage. Sprouting in onion is controlled by temperature. The temperature between 10-25°C increases sprouting. Rooting is influenced by relative humidity (RH).
More the relative humidity, more is rooting. Weight loss is more when temperature is above 35°C. Under ambient conditions the onions are stored at a temperature of 30-35° C with RH of 65-70%. In cold storage, temperature is maintained at 0-2°C while the RH is kept at 60-75%.
Sprouting is checked effectively if Maleic Hydrazide at 2500 ppm is sprayed at 75-90 days after transplanting. Effect is, however, more pronounced in kharif season than in rabi season. The storage rots could be checked if proper cleanliness is maintained in store and crop is sprayed with 0.1% Carbendazim after 90 days of transplanting and just before harvest. In India, the farmers practice different storage methods. The onions are bulk stored in special houses with thatched roof and side walls are made up with bamboo sticks or wire mesh for good air circulation. In North India, the sides are also covered with gunny cloth. Onions are stored in these sheds by spreading them on dry and damp proof floor or racks. Periodical turning of bulbs or removal of rotten, damaged and sprouted bulbs should be done. Well-ventilated improved storage structures with racks or tiers having two or three layers of bulbs would be desirable for proper storage.
The salient features of improved storage structures are as below
• Construction of storage godown on raised platform helps in reduction of moisture and dampness
• Use of Mangalore tiles roof or other suitable material prevents built up of high temperature inside.
• Increased centre height and more slope is better for air circulation and preventing humid microclimate inside godown.
• Bottom ventilation provides free and faster air circulation to avoid formation of hot and humid pockets between the onion layers.
• Avoid direct sunlight on onion bulbs to reduce sunscald, fading of colour and quality deterioration.
• Restriction on width of each stack to 60-70 cm for cool humid weather, 75-90 cm for mild and humid weather and 90-120 cm for mild and dry weather conditions
• Restriction of stacking height to 100 cm for small and multiplier onion and hot weather and 120 cm for mild weather and for big onion to avoid pressure bruising.
• Cubicles should be made instead of continuous stack leaving sufficient space for ventilation from all the sides.
One cubic metre area of store accommodates about 750 kg onions.
Transport
Onion stocks are transported in bullock carts, tractor trolleys and trucks as also railway wagons are used for longer distance movement within the country. Onions are transported in ventilated ships as well as sailing vessels / motorboats for export to Gulf and South-East Asian countries. It is also shipped in 3.5m containers or 7m containers by loading on ships.
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2.1 Pre-harvest Operations
The condition of onion leaves is a good indicator of the maturity and general state of the bulb. Bulb onions which are to be stored should be allowed to mature fully before harvest and this occurs when the leaves bend just above the top of the bulb and fall over. As a practical guide, farmers should conduct sample counts on the number of bulbs, which have fallen over in a field; and when the percentage of bulbs, which have fallen over, reaches about 70-80% then the entire crop should be harvested. Harvesting could commence earlier when 50-80% of the tops have gone over, before it is possible to see split skins exposing onion flesh Storage losses at optimum maturity are normally lower than those harvested before the tops collapse. Bulbs generally mature within 100-140 days from sowing, depending on the cultivar and the weather.
Spring onions mature for harvesting after 35-45 days from sowing. Harvested crop should be allowed to dry or cure and ripen in the sun for several days after lifting. Onions can yield up to 5 t.ha-1 under good growing and management conditions.
2.2 Harvesting & Transport
Manual harvesting is the most common practice in most developing countries. This is normally carried out by levering the bulbs with a fork to loosen them and pulling the tops by hand. In developed countries, especially in large scale farms, mechanical harvesting is commonly used. The harvesting techniques adopted are influenced by weather condition at harvest time. In areas where warm, dry weather occurs reliably, the curing and bagging of the crop can be done in the field (two phase harvesting). In wetter, temperate regions, mechanical harvesting and artificial heating and ventilation for drying are essential for reliable production of high quality bulbs on a large scale.
The following steps are followed during two-phase harvesting of onions: (a) mowing the leaves (if necessary); (b) stubbing, undercutting and sieving the onions to remove stones and clods; (c) roll the soil in the row to get a plane surface; (d) drying the bulbs (windrowing) 8 to 10 days in the field; (e) turning the bulbs 1 to 2 times; (f) harvesting, sieving and hand-grading, overloading into a trailer or in crates; and (g) transport. For one phase harvesting usually commercial potato harvesters have been adapted. After mowing the leaves the crop is immediately harvested, sieved, hand graded and loaded onto the trailer. Because of the additional operations involved, labour costs for two-phase harvesting are about 30 to 100 % higher than for one phase harvesting. The main disadvantage of one-phase harvesting is the high energy consumption required for mechanical drying. Using combine harvesting, the standardised working hours has been calculated to be 2.7 to 2.9 hr.ha-1 for stubbing, 2.4 to 2.6 hr.ha-1 for turning and 8.9 to 11 hr.ha-1 (KTBL, 1993).
Harvested bulbs are placed in containers (basket, bins) or tied into bunches and placed directly on the floor of a trailer for transport. These trailers can be pulled by an animals (such as donkey) or mechanical transport such as a tractor. Both packaging and transport systems must be selected to ensure minimum handling damage to produce. Hard surfaces should be cushioned with leaves, foam or other appropriate force decelerators.
2.3 Curing & Drying
Both curing and drying remove excess moisture from the outer layers of the bulb prior to storage. The dried skin provides a surface barrier to water loss and microbial infection, thereby preserving the main edible tissue in a fresh state. Drying also reduces shrinkage during subsequent handling, reduces the occurrence of sprouting, and allows the crop to ripen before fresh consumption or long-term storage (Opara and Geyer, 1999). This process of dehydration is sometimes called ‘curing’, but the use of the word ‘curing’ for onion drying is rather inaccurate since no cell regeneration or wound healing occurs as in other root crops such as yam and cassava. Drying reduces bulb weight and since they are sold mostly on a weight basis, achieving the desired level of dehydration is critical. Weight losses of 3-5% are normal under ambient drying conditions and up to 10 % with artificial drying.
In traditional small-scale operations, onion drying is carried out in the field in a process commonly called ‘windrowing’. It involves harvesting the mature bulbs and laying them on their sides (in windrows) on the surface of the soil to dry for 1 or 2 weeks. In hot tropical climates, the bulbs should be windrowed in such a way to reduce the exposed surface to minimise damage due to direct exposure to the sun. In wet weather, the bulbs can take longer time to dry and may develop higher levels of rots during storage. The side of the bulb in contact with wet soil or moisture may also develop brown strains or pixels, which reduce the appearance quality and value. Obviously, successful windrowing is weather dependent and therefore cannot be relied upon for large scale commercial onion production business. Bulbs harvested for storage require in total 14-20 days of ripening or drying before being stored. Harvested onions may also be placed in trays, which are then stacked at the side of the field to dry. In some tropical regions, the bulbs are tied together in groups by plaiting the tops, which are then hung over poles in sheds to dry naturally.
Harvested bulbs can also be taken straight from the field and dried artificially either in a store, shed, barns, or in a purpose-built drier. This method is commonly used when crops are stored in bulk but it can also be applied to bags, boxed or bins. Under this method, bulbs are laid on racks and heated air is rapidly passed across the surface of the bulbs night and day [O’Connor, 1979; Brice et al., 1997]. Drying may take 7-10 days and is considered complete when the necks of the bulbs have dried out and are tight and the skins shriek when held in the hand. The control of humidity level in the store is critical. Under very high humidity, drying is delayed and fungal infection can increase. However, if relative humidity is too low (below 60%), excessive water loss and splitting of the bulb outer skins can occur, resulting in storage losses and reduction of bulb value. Placing onions on wire mesh in well ventilated conditions and using air at about 30°C, 60-75% rh and 150 m³.h-1.m-3 is generally recommended for mechanical drying of onions.
2.4 Cleaning
Freedom from any impurity, which may materially alter the appearance or eating quality, is essential. Soil and other foreign materials must be removed and badly affected produce must be discarded. Cleaning may be carried out using air or by manually removing unwanted materials on the bulb surface.
Care should be taken to avoid physical injury on the bulb during these operations.
2.5 Packaging
General Information
Good packaging for onions must meet the following criteria: (a) strong enough to retain the required weight of onions under the conditions of transport and storage, (b) allow sufficient ventilation for the air around the bulbs to maintain relative humidity in the required range, and (c) in many circumstances, provide a means of displaying legally required and commercially necessary information (Brice et al., 1999).
There are many traditional methods of holding onions for transportation and/or storage that do not fit into conventional packaging classifications. These include 'string of onions', shelves and loose bulk In 'string of onions' packing, the bulbs are tied together by means of their tops to produce a bunch of bulbs is also a form of packaging. This is suitable for transporting small quantity of crop, and during storage, the bunches are hung from the roof or from special racks. Shelves for onion handling and storage are made from either wooden slats or metal mesh on a wooden or metal frame, and are usually fixed in position with the bulbs loaded and unloaded in the store.
Ventilation (natural or forced) is usually achieved by passing air over the shelves. To achieve adequate aeration of the bulbs, the depth of bulbs on the shelves should be limited to 10 cm.
Onions are also stored loose bulk (instead of containers) by heaping the bulbs directly on the floor or elevated platform. Because they are not restrained, the bulbs roll during store loading to completely fill the storage space. Bulk storage permits maximum utilisation of store space, and uniform aeration is easier to achieve than in stacks of bags or other rigid packaging.
However, where bulk storage is to implemented, the retaining walls must be strengthened when storing larger quantities of bulbs, and arrangements need to be made for rebagging before subsequent marketing. It is also difficult to inspect bulbs regularly under these storage conditions. Loose bulk handling of onion is most suitable for large-scale operations where forced ventilation can be provided during long-term storage. Soft cultivars (which are also generally sweet) 'Vidalia Sweets' should not be stored in loose bulk because of their high susceptibility to compression and impact damage.
Onions can be packaged and stored in a variety of containers such as boxes, cartons, bags, bulk bins, pre-packs, plastic film bags, and stretch-wrapped trays. Packages typically contain 25 kg and above, especially for transporting crop from field to store and/or during storage. The same 25 kg bags or smaller bags may be used from store to market place. Decision on which type of packaging to use depends on crop size, length of storage and marketing requirements. A problem with packaging onions in boxes, net bags and bulk bins is that if they are too large, and airflow pattern tends to be around rather than through them. Under this condition, the respiration heat of the bulb results in a warm, humid environment in the centre of the package, which can result in decay or sprouting. To avoid these problems in large stores, the capital investment in packaging may be quite substantial.
Onion Bags
Sacks and nets used for onion packaging fall into three groups: (i) general-purpose jute sacks, as used for many agricultural commodities, (ii) open-weave sacks of sisal-like fibre, (iii) open-mesh nets, normally of plastic materials and (iv) big bags, used alternatively to crates, containing up to 1000 kg . Jute sacks are readily available in most developing countries, but their disadvantages include: (i) generally too large - may contain 100 kg onions, hence difficult to handle and an increased risk of mechanical damage; (ii) bulbs are not visible through the fabric, and it is difficult to monitor condition during storage; (iii) there is some resistance to airflow if they are used in an aerated store; (iv) difficult to label effectively; and (v) recycled sacks may encourage spread of post harvest diseases.
Sisal sacks are made from sisal-like hard fibres and have an open weave, with thick threads spaced between about 10 and 15 cm apart. The rough nature of the fibre provides a sufficiently stable weave. These sacks are similar to jute sacks, but will allow limited visibility of the onions and impedance to airflow is less.
Open-mesh nets are the most widely used package for onions, and they are normally red or orange in colour. The slippery nature of plastics can result in the movement of the threads allowing large holes to open up. To overcome this problem, alternative nets are industrially produced to give fully stable mesh and stronger bag. The principal techniques include: (i) using extruded net from high-density PVC, (ii) knitted (warp-knitted) and asymmetric construction, and (iii) special weave in which weft threads are double, and twisted. They are also slowly degraded by sunlight, and should not be left outdoors for long period before use. In comparison with the other types of bags, they offer several advantages, including: (i) light weight, small bulk when empty, (ii) usually available in 12.5 and 25 kg sizes, (iii) fairly good visibility of bulbs, (iv) excellent ventilation, (v) hygienic, (vi) easy closing (draw-string types only), (vii) and crop brand and marketing information may be printed around the middle of the bag for easy identification.
Rigid Packages
A range of rigid containers is used to package onions for transportation, marketing, and/or storage (Opara and Geyer, 1999). The principal rigid containers are trays (10-15 kg of onions each), boxes (up to 25 kg), and bulk bins (up to 1000 kg). These types of packaging enable segregation of onions into different cultivars or sources. Choice of packaging material is important as wooden bins, for example, are liable to termite attack, and weathering during off-season. Rigid containers are also expensive, need regular maintenance and a forklift is required for handling larger containers. Where rigid containers are used for onion storage, building design is simpler than that for large-scale loose bulk storage as reinforcement of retaining walls are not required to support the bulbs. Handling damage of bulbs during filling and emptying can be high, but damage is reduced during store loading and unloading operations in comparison with loose bulk handling and storage.
Stacking of containers must be carried out with care and to ensure that the ventilation air is forced through the containers of bulbs and not around them. One of the main advantages of rigid containers is that they facilitate regular inspection of produce, and when problems occur with the stack, the area affected is often limited to a few trays, boxes or bins which may be more easily isolated and removed than in loose bulk handling system.
Onion Pre-packs
Onions are commonly sold in retail outlets in pre-packs with a capacity of 0.5-1.5 kg. Pre-packing offers the following advantages over single bulbs in heaps or bags: (i) price can be attached to produce, (ii) the collation of a number of pieces into one unit of sale may promote sale of a larger quantity than would be purchased otherwise, (iii) provides a clean odourless unit for the customer to handle, and (iv) reduces time spent at the check-out. The use of weight/price labelling machines and bar-coding has reduced the need to pack to fixed nominal weights. During preparation for retail, the quantity of produce is measured by hand or machine and filled into the pack. Then the actual weight and price and/or bar-code are automatically calculated and printed on a label, which is attached to the package. This mechanised weighing and labelling system assists the packer in accurate record keeping and avoids losses due to inaccurate pack weights. The three main types of onion pre-packs are nets, plastic film bags, and stretch-wrapped trays
2.6 Bulk Storage
General Requirements
The objectives of onion storage are to extend the period of availability of crop, maintain optimum bulb quality and minimise losses from physical, physiological, and pathological agents. Bulbs selected for storage should be firm and the neck dry and thin. Discard thick-necked bulbs because they are most likely to have high moisture content than optimum for storage, and therefore would have short storage life. Skin colour should be typical of the cultivar. Microbial infections such as Aspergillus niger occur during production of onions but these will only develop on the bulbs during storage where the storage environment is conducive for their growth. Prior to storage, crop must be cleaned and graded, and all damaged or diseased bulbs removed.
Careful harvest and pre-storage treatments with minimal mechanical loads are important to achieve a long storage period. Both store room temperature, relative humidity, and atmospheric composition affect the length of storage that can be achieved. Several technology options are available for bulk storage of onions, including low-temperate storage, high-temperature storage, ‘direct harvest’ storage and the use of controlled atmosphere (CA) stores. The recommended storage conditions under these systems are summarised below.
Storage at Low Temperature
For successful low temperature storage, good ventilation and a low level humidity in the range of 70-75% is essential. To maintain good quality crop, the period of storage varies but may be up to 200 days. For maximum storage period and minimum losses bulbs should be fully mature at harvest, and dried until the ‘neck’ of the bulb is tight. For large-scale commercial storage, onions are usually stored under refrigeration and the most commonly recommended conditions are 0°C with 70-75% rh. Regular ventilation and monitoring of both temperature and relative humidity in the store are necessary to avoid significant fluctuations in environmental conditions. During the first few days of storage the fans should provide an adequate airflow, to remove water in the outer skins and to dry bruises. High air speed is needed for a period of up to 1 week, until the skin of the upper onion layers in the bulk rustles. Excessive humidity in-store will lead to the development of roots and promote rotting while higher temperatures will result in sprouting and promote development of pathological disorders such as Botrytis rots (Thompson, 1982) Bulbs freeze below -3°C and a range of storage temperatures and relative humidities have been recommended for safe storage of onions (Table 5). Spring (green) onions store best at about 0°C and very high humidity (95%) (Table 6). The maximum length of storage under these conditions varies from just a few days to about 3 weeks.
Ventilation must be carefully applied inside the store to achieve the required temperature and humidity levels without inducing condensation of water on the surface.
Onion Storage at High-temperature
Onions can be stored at high temperatures of over 25°C at a range of relative humidities (75-85%) which is necessary for minimising water loss.
Storage at temperatures of 25-30°C has been shown to reduce sprouting and root growth compared to low-temperature storage (10-20°C). However, weight loss, desiccation of bulbs, and rots occurred at high temperatures, making the system uneconomic for long periods of storage that is required for successful onion marketing (Thompson et al., 1972; Stow, 1975). In tropical climates, high-temperature storage of onions can be achieved under both ambient and heated storage conditions. Under these conditions, ventilation must be carefully applied inside the store to achieve the required temperature and humidity levels.
‘Direct Harvest’ Storage
The need to cure onions can pose considerable challenges in situations where the climatic condition is unpredictable during the harvest period. To overcome these problems, the 'direct harvest system' has been developed and used extensively, particularly by growers in the UK, since the early 1980s. The bulbs are harvested while green, topped, loaded into store, dried and cured using well controlled ventilation system, and thereafter held in long-term low-temperature storage as required (Table 7). During stage I, removal of excessive surface moisture is achieved at high airflow rates, ignoring the rh of the air. Stage II is completed when the skins have been cured on the bulb. Adequate control of the storage condition at the various stages is critical to the success of this storage system in maintaining required bulb quality.
A is used in combination with coldstorage to extend the storage life of onions. Recommended air composition and temperature regimes are summarised in Table 8. Spring onions generally tolerate higher CO2 and O2 levels than bulb onions, and the levels of CO2 and O2 combination required varies depending on the storage temperature (Table 9). Commercial CA storage of onion bulbs is limited partly because of variable success and inconsistent effects on bulb quality. However, high carbon dioxide (0-5%) and low oxygen (1-3%) levels in combination with low temperature storage has been shown to reduce sprouting and root growth (SeaLand, 1991; Hardenburg et al., 1990). The combination of CA storage (5% CO2, 3% O2) and refrigerated storage (1°C) also resulted in 99% of the onion bulbs considered marketable after 7 months storage; however, 9% weight loss occurred (Smittle, 1989).
Onion response to CA storage varies among cultivars. Therefore, experiments should therefore be conducted under local conditions to determine the appropriate level of gas composition suitable for safe storage of local cultivars. CA storage generally increases the pungency of characteristic cultivars. For the 'Viladia Sweets' which are known for their sweetness and low pungency, the recommended storage conditions are (Smittle, 1989): 1 ºC, 70-80% rh, 3% O2, 5% CO2, 92% N2, and ventilation rate of 5.m3.h-1.m3 of onions.
2.7 Processing
Onion bulbs are generally chopped into desired sizes and shapes using a knife. Many commercial devices are also available for chopping onions. In some food preparations, the onions are blended with other ingredients to produce the desired flavour.
The only post-harvest treatment required for the long storage of bulb onions is a thorough curing of the bulbs. Curing is a drying process intended to dry off the necks and outer scale leaves of the bulbs to prevent the loss of moisture and the attack by decay during storage. The essentials for curing are heat and good ventilation, preferably with low humidity. This dries out the neck and the two or three outer layers of the bulb. The outermost layer, which may be contaminated with soil, usually falls away easily when the bulbs are cured, exposing the dry under-layer, which should have an attractive appearance. Onions are considered cured when neck is tight and the outerscales are dried until they rustle. This condition is reached when onions have lost 3 to 5% of their weight.
If onions cannot be dried in the field, they can be collected in trays, which are then stacked in a warm, covered area with good ventilation.
In cool, damp climates, onions in bulk ventilated stores are dried with artificial heat blown through the bulk at a duct temperature of 30 degrees Celsius.
Onions can also be cured by tying the tops of the bulbs in bunches and hanging them on a horizontal pole in a well-ventilated shades. Curing in shade improves bulb colour and reduces losses significantly during storage
Grading
Onions after curing are graded manually before they go in to storage or for marketing. The thick neck, bolted, doubles, injured and decayed bulbs are picked out so also misshapen small bulbs. Sorting and grading is done after storage also to fetch better price. The outer dry scales usually rub off during the grading process, giving the onions a better appearance for market. It has been experienced that if storage is arranged after proper sorting and grading losses in storage are reduced.
For local market the onions are graded based on their size.
Extra large onion (>6 cm dia.)
Medium (4-6 cm dia.)
Small (2-4 cm dia.)
The extra large onions have great demand and fetches very good price.
General Characteristics
The bulbs shall:
• be reasonably uniform in shape, size colour and pungency of the variety /type
• be mature, solid in feel, reasonably firm with tough clinging skins.
• be throughout cured and dried.
• be free from dust and other foreign material.
• be free from defective, diseased, decayed and damaged bulbs caused by seed stems, tops
• oots, moisture, dry sun scald burn, sprouting, mechanical or other injuries and staining.
• be free from moulds, soft rot and insect attack.
• % of seed stem or bolted bulbs shall not exceed 20% in Nasik kharif onions.
Bangalore and Krishnapuram onions will be free from bottle necks or doubles.
Grade designations and definitions of quality for export of onions:
Different size but not below 15
1. Tolerance for size in big onions: For accidental errors in sizing, not more than 5 % by weight of the bulbs in any lot may be of next lower grade than the minimum diameter prescribed in Nasik, Saurashtra, Bellary or Poona onions. In case of Podisu, this error in sizing not more than 10 % by weight. In this case, smallest onion in bunch would be taken for measuring the diameter.
2. Defective, diseased and damaged shall mean malformed bulbs and the bulbs internally or externally damaged, diseased or discoloured material affecting the quality. The decayed onions shall not exceed 2% in any lot.
General: The grade shall be allowed to be packed only against irrevocable letter of credit.
# NS grade: This is not a grade in its strict sense but has been provided for the onions not covered under regular grade. Onions under this grade shall be exported only against a specific order from foreign buyer inducting the quality.
Packaging
Packing should be small for easy handling during transit and may vary according to market demand. Onions are packed in jute (hessian) bags for transporting to yard or brought as loose. For safe handling, 40 kg open mesh jute bags having 200-300 g weight should be used in domestic market. For export, common big onions are packed in 5-25 kg size open mesh jute bags.
Bangalore Rose and multiplier onions are packed for export in 14-15 kg wooden baskets. Nylon net bags, when used for packing have resulted in less storage loss because of good ventilation.
Handling
Bulbs intended for storage must be free from cuts and handled with extreme care. Onions should not be dropped on to non-resilient surface from more than 6 feet height. If onions are to be stacked after packing in store or trucks, the better height is 2-2.5 metres. Losses due to rot is reported to be more if onions are stored in gunny bags than in loose or wooden crates.
Storage
Proper storage of bulbs is necessary both for consumption and also for seed production. Onions should not be stored unless adequately dried either in the field or by artificial means. It is necessary to dry the neck tissue and outer scales until they rustle when handled otherwise the bulbs will rot in storage. Sprouting in onion is controlled by temperature. The temperature between 10-25°C increases sprouting. Rooting is influenced by relative humidity (RH).
More the relative humidity, more is rooting. Weight loss is more when temperature is above 35°C. Under ambient conditions the onions are stored at a temperature of 30-35° C with RH of 65-70%. In cold storage, temperature is maintained at 0-2°C while the RH is kept at 60-75%.
Sprouting is checked effectively if Maleic Hydrazide at 2500 ppm is sprayed at 75-90 days after transplanting. Effect is, however, more pronounced in kharif season than in rabi season. The storage rots could be checked if proper cleanliness is maintained in store and crop is sprayed with 0.1% Carbendazim after 90 days of transplanting and just before harvest. In India, the farmers practice different storage methods. The onions are bulk stored in special houses with thatched roof and side walls are made up with bamboo sticks or wire mesh for good air circulation. In North India, the sides are also covered with gunny cloth. Onions are stored in these sheds by spreading them on dry and damp proof floor or racks. Periodical turning of bulbs or removal of rotten, damaged and sprouted bulbs should be done. Well-ventilated improved storage structures with racks or tiers having two or three layers of bulbs would be desirable for proper storage.
The salient features of improved storage structures are as below
• Construction of storage godown on raised platform helps in reduction of moisture and dampness
• Use of Mangalore tiles roof or other suitable material prevents built up of high temperature inside.
• Increased centre height and more slope is better for air circulation and preventing humid microclimate inside godown.
• Bottom ventilation provides free and faster air circulation to avoid formation of hot and humid pockets between the onion layers.
• Avoid direct sunlight on onion bulbs to reduce sunscald, fading of colour and quality deterioration.
• Restriction on width of each stack to 60-70 cm for cool humid weather, 75-90 cm for mild and humid weather and 90-120 cm for mild and dry weather conditions
• Restriction of stacking height to 100 cm for small and multiplier onion and hot weather and 120 cm for mild weather and for big onion to avoid pressure bruising.
• Cubicles should be made instead of continuous stack leaving sufficient space for ventilation from all the sides.
One cubic metre area of store accommodates about 750 kg onions.
Transport
Onion stocks are transported in bullock carts, tractor trolleys and trucks as also railway wagons are used for longer distance movement within the country. Onions are transported in ventilated ships as well as sailing vessels / motorboats for export to Gulf and South-East Asian countries. It is also shipped in 3.5m containers or 7m containers by loading on ships.
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2.1 Pre-harvest Operations
The condition of onion leaves is a good indicator of the maturity and general state of the bulb. Bulb onions which are to be stored should be allowed to mature fully before harvest and this occurs when the leaves bend just above the top of the bulb and fall over. As a practical guide, farmers should conduct sample counts on the number of bulbs, which have fallen over in a field; and when the percentage of bulbs, which have fallen over, reaches about 70-80% then the entire crop should be harvested. Harvesting could commence earlier when 50-80% of the tops have gone over, before it is possible to see split skins exposing onion flesh Storage losses at optimum maturity are normally lower than those harvested before the tops collapse. Bulbs generally mature within 100-140 days from sowing, depending on the cultivar and the weather.
Spring onions mature for harvesting after 35-45 days from sowing. Harvested crop should be allowed to dry or cure and ripen in the sun for several days after lifting. Onions can yield up to 5 t.ha-1 under good growing and management conditions.
2.2 Harvesting & Transport
Manual harvesting is the most common practice in most developing countries. This is normally carried out by levering the bulbs with a fork to loosen them and pulling the tops by hand. In developed countries, especially in large scale farms, mechanical harvesting is commonly used. The harvesting techniques adopted are influenced by weather condition at harvest time. In areas where warm, dry weather occurs reliably, the curing and bagging of the crop can be done in the field (two phase harvesting). In wetter, temperate regions, mechanical harvesting and artificial heating and ventilation for drying are essential for reliable production of high quality bulbs on a large scale.
The following steps are followed during two-phase harvesting of onions: (a) mowing the leaves (if necessary); (b) stubbing, undercutting and sieving the onions to remove stones and clods; (c) roll the soil in the row to get a plane surface; (d) drying the bulbs (windrowing) 8 to 10 days in the field; (e) turning the bulbs 1 to 2 times; (f) harvesting, sieving and hand-grading, overloading into a trailer or in crates; and (g) transport. For one phase harvesting usually commercial potato harvesters have been adapted. After mowing the leaves the crop is immediately harvested, sieved, hand graded and loaded onto the trailer. Because of the additional operations involved, labour costs for two-phase harvesting are about 30 to 100 % higher than for one phase harvesting. The main disadvantage of one-phase harvesting is the high energy consumption required for mechanical drying. Using combine harvesting, the standardised working hours has been calculated to be 2.7 to 2.9 hr.ha-1 for stubbing, 2.4 to 2.6 hr.ha-1 for turning and 8.9 to 11 hr.ha-1 (KTBL, 1993).
Harvested bulbs are placed in containers (basket, bins) or tied into bunches and placed directly on the floor of a trailer for transport. These trailers can be pulled by an animals (such as donkey) or mechanical transport such as a tractor. Both packaging and transport systems must be selected to ensure minimum handling damage to produce. Hard surfaces should be cushioned with leaves, foam or other appropriate force decelerators.
2.3 Curing & Drying
Both curing and drying remove excess moisture from the outer layers of the bulb prior to storage. The dried skin provides a surface barrier to water loss and microbial infection, thereby preserving the main edible tissue in a fresh state. Drying also reduces shrinkage during subsequent handling, reduces the occurrence of sprouting, and allows the crop to ripen before fresh consumption or long-term storage (Opara and Geyer, 1999). This process of dehydration is sometimes called ‘curing’, but the use of the word ‘curing’ for onion drying is rather inaccurate since no cell regeneration or wound healing occurs as in other root crops such as yam and cassava. Drying reduces bulb weight and since they are sold mostly on a weight basis, achieving the desired level of dehydration is critical. Weight losses of 3-5% are normal under ambient drying conditions and up to 10 % with artificial drying.
In traditional small-scale operations, onion drying is carried out in the field in a process commonly called ‘windrowing’. It involves harvesting the mature bulbs and laying them on their sides (in windrows) on the surface of the soil to dry for 1 or 2 weeks. In hot tropical climates, the bulbs should be windrowed in such a way to reduce the exposed surface to minimise damage due to direct exposure to the sun. In wet weather, the bulbs can take longer time to dry and may develop higher levels of rots during storage. The side of the bulb in contact with wet soil or moisture may also develop brown strains or pixels, which reduce the appearance quality and value. Obviously, successful windrowing is weather dependent and therefore cannot be relied upon for large scale commercial onion production business. Bulbs harvested for storage require in total 14-20 days of ripening or drying before being stored. Harvested onions may also be placed in trays, which are then stacked at the side of the field to dry. In some tropical regions, the bulbs are tied together in groups by plaiting the tops, which are then hung over poles in sheds to dry naturally.
Harvested bulbs can also be taken straight from the field and dried artificially either in a store, shed, barns, or in a purpose-built drier. This method is commonly used when crops are stored in bulk but it can also be applied to bags, boxed or bins. Under this method, bulbs are laid on racks and heated air is rapidly passed across the surface of the bulbs night and day [O’Connor, 1979; Brice et al., 1997]. Drying may take 7-10 days and is considered complete when the necks of the bulbs have dried out and are tight and the skins shriek when held in the hand. The control of humidity level in the store is critical. Under very high humidity, drying is delayed and fungal infection can increase. However, if relative humidity is too low (below 60%), excessive water loss and splitting of the bulb outer skins can occur, resulting in storage losses and reduction of bulb value. Placing onions on wire mesh in well ventilated conditions and using air at about 30°C, 60-75% rh and 150 m³.h-1.m-3 is generally recommended for mechanical drying of onions.
2.4 Cleaning
Freedom from any impurity, which may materially alter the appearance or eating quality, is essential. Soil and other foreign materials must be removed and badly affected produce must be discarded. Cleaning may be carried out using air or by manually removing unwanted materials on the bulb surface.
Care should be taken to avoid physical injury on the bulb during these operations.
2.5 Packaging
General Information
Good packaging for onions must meet the following criteria: (a) strong enough to retain the required weight of onions under the conditions of transport and storage, (b) allow sufficient ventilation for the air around the bulbs to maintain relative humidity in the required range, and (c) in many circumstances, provide a means of displaying legally required and commercially necessary information (Brice et al., 1999).
There are many traditional methods of holding onions for transportation and/or storage that do not fit into conventional packaging classifications. These include 'string of onions', shelves and loose bulk In 'string of onions' packing, the bulbs are tied together by means of their tops to produce a bunch of bulbs is also a form of packaging. This is suitable for transporting small quantity of crop, and during storage, the bunches are hung from the roof or from special racks. Shelves for onion handling and storage are made from either wooden slats or metal mesh on a wooden or metal frame, and are usually fixed in position with the bulbs loaded and unloaded in the store.
Ventilation (natural or forced) is usually achieved by passing air over the shelves. To achieve adequate aeration of the bulbs, the depth of bulbs on the shelves should be limited to 10 cm.
Onions are also stored loose bulk (instead of containers) by heaping the bulbs directly on the floor or elevated platform. Because they are not restrained, the bulbs roll during store loading to completely fill the storage space. Bulk storage permits maximum utilisation of store space, and uniform aeration is easier to achieve than in stacks of bags or other rigid packaging.
However, where bulk storage is to implemented, the retaining walls must be strengthened when storing larger quantities of bulbs, and arrangements need to be made for rebagging before subsequent marketing. It is also difficult to inspect bulbs regularly under these storage conditions. Loose bulk handling of onion is most suitable for large-scale operations where forced ventilation can be provided during long-term storage. Soft cultivars (which are also generally sweet) 'Vidalia Sweets' should not be stored in loose bulk because of their high susceptibility to compression and impact damage.
Onions can be packaged and stored in a variety of containers such as boxes, cartons, bags, bulk bins, pre-packs, plastic film bags, and stretch-wrapped trays. Packages typically contain 25 kg and above, especially for transporting crop from field to store and/or during storage. The same 25 kg bags or smaller bags may be used from store to market place. Decision on which type of packaging to use depends on crop size, length of storage and marketing requirements. A problem with packaging onions in boxes, net bags and bulk bins is that if they are too large, and airflow pattern tends to be around rather than through them. Under this condition, the respiration heat of the bulb results in a warm, humid environment in the centre of the package, which can result in decay or sprouting. To avoid these problems in large stores, the capital investment in packaging may be quite substantial.
Onion Bags
Sacks and nets used for onion packaging fall into three groups: (i) general-purpose jute sacks, as used for many agricultural commodities, (ii) open-weave sacks of sisal-like fibre, (iii) open-mesh nets, normally of plastic materials and (iv) big bags, used alternatively to crates, containing up to 1000 kg . Jute sacks are readily available in most developing countries, but their disadvantages include: (i) generally too large - may contain 100 kg onions, hence difficult to handle and an increased risk of mechanical damage; (ii) bulbs are not visible through the fabric, and it is difficult to monitor condition during storage; (iii) there is some resistance to airflow if they are used in an aerated store; (iv) difficult to label effectively; and (v) recycled sacks may encourage spread of post harvest diseases.
Sisal sacks are made from sisal-like hard fibres and have an open weave, with thick threads spaced between about 10 and 15 cm apart. The rough nature of the fibre provides a sufficiently stable weave. These sacks are similar to jute sacks, but will allow limited visibility of the onions and impedance to airflow is less.
Open-mesh nets are the most widely used package for onions, and they are normally red or orange in colour. The slippery nature of plastics can result in the movement of the threads allowing large holes to open up. To overcome this problem, alternative nets are industrially produced to give fully stable mesh and stronger bag. The principal techniques include: (i) using extruded net from high-density PVC, (ii) knitted (warp-knitted) and asymmetric construction, and (iii) special weave in which weft threads are double, and twisted. They are also slowly degraded by sunlight, and should not be left outdoors for long period before use. In comparison with the other types of bags, they offer several advantages, including: (i) light weight, small bulk when empty, (ii) usually available in 12.5 and 25 kg sizes, (iii) fairly good visibility of bulbs, (iv) excellent ventilation, (v) hygienic, (vi) easy closing (draw-string types only), (vii) and crop brand and marketing information may be printed around the middle of the bag for easy identification.
Rigid Packages
A range of rigid containers is used to package onions for transportation, marketing, and/or storage (Opara and Geyer, 1999). The principal rigid containers are trays (10-15 kg of onions each), boxes (up to 25 kg), and bulk bins (up to 1000 kg). These types of packaging enable segregation of onions into different cultivars or sources. Choice of packaging material is important as wooden bins, for example, are liable to termite attack, and weathering during off-season. Rigid containers are also expensive, need regular maintenance and a forklift is required for handling larger containers. Where rigid containers are used for onion storage, building design is simpler than that for large-scale loose bulk storage as reinforcement of retaining walls are not required to support the bulbs. Handling damage of bulbs during filling and emptying can be high, but damage is reduced during store loading and unloading operations in comparison with loose bulk handling and storage.
Stacking of containers must be carried out with care and to ensure that the ventilation air is forced through the containers of bulbs and not around them. One of the main advantages of rigid containers is that they facilitate regular inspection of produce, and when problems occur with the stack, the area affected is often limited to a few trays, boxes or bins which may be more easily isolated and removed than in loose bulk handling system.
Onion Pre-packs
Onions are commonly sold in retail outlets in pre-packs with a capacity of 0.5-1.5 kg. Pre-packing offers the following advantages over single bulbs in heaps or bags: (i) price can be attached to produce, (ii) the collation of a number of pieces into one unit of sale may promote sale of a larger quantity than would be purchased otherwise, (iii) provides a clean odourless unit for the customer to handle, and (iv) reduces time spent at the check-out. The use of weight/price labelling machines and bar-coding has reduced the need to pack to fixed nominal weights. During preparation for retail, the quantity of produce is measured by hand or machine and filled into the pack. Then the actual weight and price and/or bar-code are automatically calculated and printed on a label, which is attached to the package. This mechanised weighing and labelling system assists the packer in accurate record keeping and avoids losses due to inaccurate pack weights. The three main types of onion pre-packs are nets, plastic film bags, and stretch-wrapped trays
2.6 Bulk Storage
General Requirements
The objectives of onion storage are to extend the period of availability of crop, maintain optimum bulb quality and minimise losses from physical, physiological, and pathological agents. Bulbs selected for storage should be firm and the neck dry and thin. Discard thick-necked bulbs because they are most likely to have high moisture content than optimum for storage, and therefore would have short storage life. Skin colour should be typical of the cultivar. Microbial infections such as Aspergillus niger occur during production of onions but these will only develop on the bulbs during storage where the storage environment is conducive for their growth. Prior to storage, crop must be cleaned and graded, and all damaged or diseased bulbs removed.
Careful harvest and pre-storage treatments with minimal mechanical loads are important to achieve a long storage period. Both store room temperature, relative humidity, and atmospheric composition affect the length of storage that can be achieved. Several technology options are available for bulk storage of onions, including low-temperate storage, high-temperature storage, ‘direct harvest’ storage and the use of controlled atmosphere (CA) stores. The recommended storage conditions under these systems are summarised below.
Storage at Low Temperature
For successful low temperature storage, good ventilation and a low level humidity in the range of 70-75% is essential. To maintain good quality crop, the period of storage varies but may be up to 200 days. For maximum storage period and minimum losses bulbs should be fully mature at harvest, and dried until the ‘neck’ of the bulb is tight. For large-scale commercial storage, onions are usually stored under refrigeration and the most commonly recommended conditions are 0°C with 70-75% rh. Regular ventilation and monitoring of both temperature and relative humidity in the store are necessary to avoid significant fluctuations in environmental conditions. During the first few days of storage the fans should provide an adequate airflow, to remove water in the outer skins and to dry bruises. High air speed is needed for a period of up to 1 week, until the skin of the upper onion layers in the bulk rustles. Excessive humidity in-store will lead to the development of roots and promote rotting while higher temperatures will result in sprouting and promote development of pathological disorders such as Botrytis rots (Thompson, 1982) Bulbs freeze below -3°C and a range of storage temperatures and relative humidities have been recommended for safe storage of onions (Table 5). Spring (green) onions store best at about 0°C and very high humidity (95%) (Table 6). The maximum length of storage under these conditions varies from just a few days to about 3 weeks.
Ventilation must be carefully applied inside the store to achieve the required temperature and humidity levels without inducing condensation of water on the surface.
Onion Storage at High-temperature
Onions can be stored at high temperatures of over 25°C at a range of relative humidities (75-85%) which is necessary for minimising water loss.
Storage at temperatures of 25-30°C has been shown to reduce sprouting and root growth compared to low-temperature storage (10-20°C). However, weight loss, desiccation of bulbs, and rots occurred at high temperatures, making the system uneconomic for long periods of storage that is required for successful onion marketing (Thompson et al., 1972; Stow, 1975). In tropical climates, high-temperature storage of onions can be achieved under both ambient and heated storage conditions. Under these conditions, ventilation must be carefully applied inside the store to achieve the required temperature and humidity levels.
‘Direct Harvest’ Storage
The need to cure onions can pose considerable challenges in situations where the climatic condition is unpredictable during the harvest period. To overcome these problems, the 'direct harvest system' has been developed and used extensively, particularly by growers in the UK, since the early 1980s. The bulbs are harvested while green, topped, loaded into store, dried and cured using well controlled ventilation system, and thereafter held in long-term low-temperature storage as required (Table 7). During stage I, removal of excessive surface moisture is achieved at high airflow rates, ignoring the rh of the air. Stage II is completed when the skins have been cured on the bulb. Adequate control of the storage condition at the various stages is critical to the success of this storage system in maintaining required bulb quality.
A is used in combination with coldstorage to extend the storage life of onions. Recommended air composition and temperature regimes are summarised in Table 8. Spring onions generally tolerate higher CO2 and O2 levels than bulb onions, and the levels of CO2 and O2 combination required varies depending on the storage temperature (Table 9). Commercial CA storage of onion bulbs is limited partly because of variable success and inconsistent effects on bulb quality. However, high carbon dioxide (0-5%) and low oxygen (1-3%) levels in combination with low temperature storage has been shown to reduce sprouting and root growth (SeaLand, 1991; Hardenburg et al., 1990). The combination of CA storage (5% CO2, 3% O2) and refrigerated storage (1°C) also resulted in 99% of the onion bulbs considered marketable after 7 months storage; however, 9% weight loss occurred (Smittle, 1989).
Onion response to CA storage varies among cultivars. Therefore, experiments should therefore be conducted under local conditions to determine the appropriate level of gas composition suitable for safe storage of local cultivars. CA storage generally increases the pungency of characteristic cultivars. For the 'Viladia Sweets' which are known for their sweetness and low pungency, the recommended storage conditions are (Smittle, 1989): 1 ºC, 70-80% rh, 3% O2, 5% CO2, 92% N2, and ventilation rate of 5.m3.h-1.m3 of onions.
2.7 Processing
Onion bulbs are generally chopped into desired sizes and shapes using a knife. Many commercial devices are also available for chopping onions. In some food preparations, the onions are blended with other ingredients to produce the desired flavour.
Sunday, February 5, 2012
Packing House Operations for Fruits and Vegetables
Packing houses serve as a collection centre for fruits and vegetables prior to distribution and marketing. The houses can be simple packing sheds with a limited equipment and minimal operations or a large complex that is well equipped and with facilities for specialized operations. The types of operation carried out vary with different commodities and market requirements. Produce that are destined for export or supermarket outlets are often subjected to elaborate operations compared to local markets. Some of the operations are as follows:
Sorting and Trimming
Freshly harvested fruits and vegetables are sorted for uniformity in size, shape and varietal characteristics. Damaged, discoloured and decayed parts are removed to make the produce more attractive and prevent infection from the diseased parts.
Washing
Washing is necessary to remove extraneous materials from the field such as dirts, chemicals and latex. This is usually done before storage or immediate retailing of the produce. In order to r educe the incident of decay, chlorine is often added to the wash water.
Drying
Drying is done to remove excessive moisture from the surface of the produce. Excessive drying should be avoided to prevent wilting, shrinking and water loss.
Waxing
Waxing is done on certain types of fruits and vegetables such as ginger, tomato, citrus and melons to reduce water loss, thereby reducing shriveling. In addition to that, the application of edible wax will enhance the appearance of the produce.
Curing
Injured and bruised surfaces of root, rhizome and tuberous crops are allowed to heal by holding them at ambient temperatures for a few days. Curing initiates the formation of periderm layers at wound areas, thereby reducing moisture loss and microbial infection. Sufficiently cured vegetables can be stored for a longer period.
Chemical Treatments
Fungicides and growth regulators are commonly used to reduce decay and undesirable growth respectively. The use of chemicals should be closely supervised and within the recommended levels for human consumption.
Grading
Fresh fruits and vegetables are classified into groups according to a set of recognized criteria of quality and size, with each bearing an accepted name and size grouping.
Packaging
Produce are packed in suitable containers to provide protection against mechanical and biological damages during transportation and subsequent handling operations. Packaging materials should be of accepted standards with regard to strength, ruggedness and resistance to pressure. Packages should have adequate ventilation so that produce will not warm up as a result of heat arising from respiration. Excessive ventilation, however, may result in wilting.
Pre-cooling
Pre-cooling is an essential step prior to storage at low temperatures. It is the rapid removal of field heat from the produce to reduce the rate of respiration, microbial activity and refrigeration load. Pre-cooling can be done with chilled water, ice or cool air (forced air cooling), whereby the produce is cooled to the half cooling temperature.
Storage
Storage at low temperatures has been an effective mean of extending the shelf-life of fresh fruits and vegetables. It also enables orderly marketing and distribution of produce in time of peak production. Temperature requirements for different produce may vary depending on variety, location, stage of maturity and other factors. It is important to note that cool storage is a tool used to maintain quality but not to improve it.
Transportation
Proper handling of the produce during transportation is essential to reduce losses to a minimum and to maintain their quality from the farm to the packing house and from packing house to market. The used of refrigerated trucks to transport highly perishable and high value produce will maintain their quality over an extended duration. In non ventilated vans, temperature of the fruits or vegetables rises quickly, increasing respiration and decay.
Sorting and Trimming
Freshly harvested fruits and vegetables are sorted for uniformity in size, shape and varietal characteristics. Damaged, discoloured and decayed parts are removed to make the produce more attractive and prevent infection from the diseased parts.
Washing
Washing is necessary to remove extraneous materials from the field such as dirts, chemicals and latex. This is usually done before storage or immediate retailing of the produce. In order to r educe the incident of decay, chlorine is often added to the wash water.
Drying
Drying is done to remove excessive moisture from the surface of the produce. Excessive drying should be avoided to prevent wilting, shrinking and water loss.
Waxing
Waxing is done on certain types of fruits and vegetables such as ginger, tomato, citrus and melons to reduce water loss, thereby reducing shriveling. In addition to that, the application of edible wax will enhance the appearance of the produce.
Curing
Injured and bruised surfaces of root, rhizome and tuberous crops are allowed to heal by holding them at ambient temperatures for a few days. Curing initiates the formation of periderm layers at wound areas, thereby reducing moisture loss and microbial infection. Sufficiently cured vegetables can be stored for a longer period.
Chemical Treatments
Fungicides and growth regulators are commonly used to reduce decay and undesirable growth respectively. The use of chemicals should be closely supervised and within the recommended levels for human consumption.
Grading
Fresh fruits and vegetables are classified into groups according to a set of recognized criteria of quality and size, with each bearing an accepted name and size grouping.
Packaging
Produce are packed in suitable containers to provide protection against mechanical and biological damages during transportation and subsequent handling operations. Packaging materials should be of accepted standards with regard to strength, ruggedness and resistance to pressure. Packages should have adequate ventilation so that produce will not warm up as a result of heat arising from respiration. Excessive ventilation, however, may result in wilting.
Pre-cooling
Pre-cooling is an essential step prior to storage at low temperatures. It is the rapid removal of field heat from the produce to reduce the rate of respiration, microbial activity and refrigeration load. Pre-cooling can be done with chilled water, ice or cool air (forced air cooling), whereby the produce is cooled to the half cooling temperature.
Storage
Storage at low temperatures has been an effective mean of extending the shelf-life of fresh fruits and vegetables. It also enables orderly marketing and distribution of produce in time of peak production. Temperature requirements for different produce may vary depending on variety, location, stage of maturity and other factors. It is important to note that cool storage is a tool used to maintain quality but not to improve it.
Transportation
Proper handling of the produce during transportation is essential to reduce losses to a minimum and to maintain their quality from the farm to the packing house and from packing house to market. The used of refrigerated trucks to transport highly perishable and high value produce will maintain their quality over an extended duration. In non ventilated vans, temperature of the fruits or vegetables rises quickly, increasing respiration and decay.
Saturday, February 4, 2012
PACKAGING REQUIREMENTS FOR FRESH FRUITS AND VEGETABLES
Introduction
Packaging fresh fruits and vegetables is one of the more important steps in the long and complicated journey from grower to consumer. Bags, crates, hampers, baskets, cartons, bulk bins, and palletized containers are convenient containers for handling, transporting, and marketing fresh produce. More than 1,500 different types of packages are used for produce in the U.S. and the number continues to increase as the industry introduces new packaging materials and concepts. Although the industry generally agrees that container standardization is one way to reduce cost, the trend in recent years has moved toward a wider range of package sizes to accommodate the diverse needs of wholesalers, consumers, food service buyers, and processing operations.
Packing and packaging materials contribute a significant cost to the produce industry; therefore it is important that packers, shippers, buyers, and consumers have a clear understanding of the wide range of packaging options available. This fact sheet describes some of the many types of packaging, including their functions, uses, and limitations. Also included is a listing, by commodity, of the common produce containers standard to the industry.
The Function of Packaging or Why package Produce?
A significant percentage of produce buyer and consumer complaints may be traced to container failure because of poor design or inappropriate selection and use. A properly designed produce container should contain, protect, and identify the produce, satisfying everyone from grower to consumer.
PACKAGING POINTS
Recyclability/Biodegradability.
A growing number of U.S. markets and many export markets have waste disposal restrictions for packaging materials. In the near future, almost all produce packaging will be recyclable or biodegradable, or both. Many of the largest buyers of fresh produce are also those most concerned about environmental issues.
Variety.
The trend is toward greater use of bulk packages for processors and wholesale buyers and smaller packages for consumers. There are now more than 1,500 different sizes and styles of produce packages.
Sales Appeal.High quality graphics are increasingly being used to boost sales appeal. Multi-color printing, distinctive lettering, and logos are now common.
Shelf Life.
Modern produce packaging can be custom engineered for each commodity to extend shelf life and reduce waste.
Containment
The container must enclose the produce in convenient units for handling and distribution. The produce should fit well inside the container, with little wasted space. Small produce items that are spherical or oblong (such as potatoes, onions, and apples) may be packaged efficiently utilizing a variety of different package shapes and sizes. However, many produce items such as asparagus, berries, or soft fruit may require containers specially designed for that item.
packages of produce commonly handled by hand are usually limited to 50 pounds. Bulk packages moved by fork lifts may weigh as much as 1,200 pounds.
Protection
The package must protect the produce from mechanical damage and poor environmental conditions during handling and distribution. To produce buyers, torn, dented, or collapsed produce packages usually indicate lack of care in handling the contents. Produce containers must be sturdy enough to resist damage during packaging, storage, and transportation to market.
Because almost all produce packages are palletized, produce containers should have sufficient stacking strength to resist crushing in a low temperature, high humidity environment. Although the cost of packaging materials has escalated sharply in recent years, poor quality, lightweight containers that are easily damaged by handling or moisture are no longer tolerated by packers or buyers.
Produce destined for export markets requires that containers to be extra sturdy. Air-freighted produce may require special packing, package sizes, and insulation. Marketers who export fresh produce should consult with freight companies about any special packaging requirements. Additionally, the USDA and various state export agencies may be able to provide specific packaging information.
Damage resulting from poor environmental control during handling and transit is one of the leading causes of rejected produce and low buyer and consumer satisfaction. Each fresh fruit and vegetable commodity has its own requirements for temperature, humidity, and environmental gas composition.
Produce containers should be produce friendly - helping to maintain an optimum environment for the longest shelf life. This may include special materials to slow the loss of water from the produce, insulation materials to keep out the heat, or engineered plastic liners that maintain a favorable mix of oxygen and carbon dioxide.
Identification
The package must identify and provide useful information about the produce. It is customary (and may be required in some cases) to provide information such as the produce name, brand, size, grade, variety, net weight, count, grower, shipper, and country of origin. It is also becoming more common to find included on the package, nutritional information, recipes, and other useful information directed specifically at the consumer. In consumer marketing, pack- age appearance has also become an important part of point of sale displays.
Universal Product Codes (UPC or bar codes) may be included as part of the labeling. The UPCs used in the food industry consist of a ten-digit machine readable code. The first five digits are a number assigned to the specific producer (packer or shipper) and the second five digits represent specific product information such as type of produce and size of package. Although no price information is included, UPCs are used more and more by packers, shippers, buyers, and Example of a UPC retailers as a fast and convenient method of inventory control and cost accounting. Efficient use of UPCs requires coordination with everyone who handles the package.
Types of Packaging Materials
Wood
Pallets literally form the base on which most fresh produce is delivered to the consumer. Pallets were first used during World War II as an efficient way to move goods. The produce industry uses approximately 190 of the 700 million pallets produced per year in the U.S.. About 40 percent of these are single-use pallets. Because many are of a non-standard size, the pallets are built as inexpensively as possible and discarded after a single use. Although standardization efforts have been slowly under way for many years, the efforts have been accelerated by pressure from environmental groups, in addition to the rising cost of pallets and landfill tipping fees.
Over the years, the 40-inch wide, by 48-inch long pallet has evolved as the unofficial standard size. Standardization encourages re-use, which has many benefits. Besides reducing cost because they may be used many times, most pallet racks and automated pallet handling equipment are designed for standard-size pallets. Standard size pallets make efficient use of truck and van space and can accommodate heavier loads and more stress than lighter single-use pallets. Additionally, the use of a single pallet size could substantially reduce pallet inventory and warehousing costs along with pallet repair and disposal costs. The adoption of a pallet standard throughout the produce industry would also aid efforts toward standardization of produce containers.
In the early 1950s, an alternative to the pallet was introduced. It is a pallet-size sheet (slipsheet) of corrugated fiberboard or plastic (or a combination of these materials) with a narrow lip along one or more sides. packages of produce are stacked directly on this sheet as if it were a pallet. Once the packages are in place, they are moved by a specially equipped fork lift equipped with a thin metal sheet instead of forks.
Slipsheets are considerably less expensive than pallets to buy, store, and maintain; they may be re-used many times; and they reduce the tare weight of the load. However, they require the use of a special fork-lift attachment at each handling point from packer to retailer.
Depending on the size of produce package, a single pallet may carry from 20 to over 100 individual packages. Because these packages are often loosely stacked to allow for air circulation, or are bulging and difficult to stack evenly, they must be secured (unitized) to prevent shifting during handling and transit. Although widely used, plastic straps and tapes may not have completely satisfactory results. Plastic or paper corner tabs should always be used to prevent the straps from crushing the corners of packages.
Plastic stretch film is also widely used to secure produce packages. A good film must stretch, retain its elasticity, and cling to the packages. Plastic film may conform easily to various size loads. It helps protect the packages from loss of moisture, makes the pallet more secure against pilferage, and can be applied using partial automation. However, plastic film severely restricts proper ventilation. A common alternative to stretch film is plastic netting, which is much better for stabilizing some pallet loads, such as those that require forced-air cooling. Used stretch film and plastic netting may be difficult to properly handle and recycle.
A very low-cost and almost fully automated method of pallet stabilization is the application of a small amount of special glue to the top of each package.
As the packages are stacked, the glue secures all cartons together. This glue has a low tensile strength so cartons may be easily separated or repositioned, but a high shear strength so they will not slide. The glue does not present disposal or recycling problems.
Pallet Bins. Substantial wooden pallet bins of milled lumber or.plywood are primarily used to move produce from the field or orchard to the packing house. Depending on the application, capacities may range from 12 to more than 50 bushels. Although the height may vary, the length and width is generally the same as a standard pallet (48 inches by 40 inches). More efficient double-wide pallet bins (48 inches by 80 inches) are becoming more common in some produce operations.
Most pallet bins are locally made; therefore it is very important that they be consistent from lot to lot in materials, construction, and especially size. For example, small differences in overall dimensions Pallet bin can add up to big problems when several hundred are stacked together for cooling, ventilation, or storage. It is also important that stress points be adequately reinforced.
The average life of a hardwood pallet bin that is stored outside is approximately five years. When properly protected from the weather, pallets bins may have a useful life of 10 years or more.
Uniform voluntary standards for wood pallets and other wood containers are administered by the National Wooden Pallet and Container Association, Washington, DC. Additionally, the American Society of Agricultural Engineers, St. Joseph, Michigan, publishes standards for agricultural pallet bins (ASAE S337.1).
Wire-Bound Crates. Although alternatives are available, wooden wire-bound crates are used extensively for snap beans, sweet corn and several other commodities that require hydrocooling. Wire-bound crates are sturdy, rigid and have very high stacking strength that is essentially unaffected by water.
Wire-bound crates come in many different sizes from half- bushel to pallet-bin size and have a great deal of open space to facilitate cooling and ventilation. Although few are re-used, wire-bound crates may be dissembled after use and shipped back to the packer (flat). In some areas, used containers may pose a significant disposal problem. Wirebound crates are not generally acceptable for consumer packaging because of the difficulty in affixing suitable labels.
Wooden Crates and Lugs. Wooden crates, once extensively used for apples, stone fruit, and potatoes have been almost totally replaced by other types of containers. The relative expense of the container, a greater concern for tare weight, and advances in material handling have reduced their use to a few specialty items, such as expensive tropical fruit. The 15-, 20-, and 25-pound wooden lugs still used for bunch grapes and some specialty crops are being gradually replaced with less costly alternatives.
Wooden Baskets and Hampers. Wire-reinforced wood veneer baskets and hampers of different sizes were once used for a wide variety of crops from strawberries to sweetpotatoes. They are durable and may be nested for efficient transport when empty. However, cost, disposal problems, and difficulty in efficient palletization have severely limited their use to mostly local grower markets where they may be re-used many times.
Corrugated Fiberboard
Corrugated fiberboard (often mistakenly called cardboard or pasteboard) is manufactured in many different styles and weights. Because of its relativity low cost and versatility, it is the dominant produce container material and will probably remain so in the near future. The strength and serviceability of corrugated fiberboard have been improving in recent years.
Most corrugated fiberboard is made from three or more layers of paperboard manufactured by the kraft process. To be considered paperboard, the paper must be thicker than 0.008 inches. The grades of paperboard are differentiated by their weight (in pounds per 1,000 square feet) and their thickness. Kraft paper made from unbleached pulp has a characteristic brown color and is exceptionally strong. In addition to virgin wood fibers, Kraft paper may have some portion of synthetic fibers for additional strength, sizing (starch), and other materials to give it wet strength and printability.
Most fiberboard contains some recycled fibers. Minimum amounts of recycled materials may be specified by law and the percentage is expected to increase in the future. Tests have shown that cartons of fully recycled pulp have about 75 percent of the stacking strength of virgin fiber containers. The use of recycled fibers will inevitably lead to the use of thicker walled containers.
Double-faced corrugated fiberboard is the predominant form used for produce containers. It is produced by sandwiching a layer of corrugated paperboard between an inner and outer liner (facing) of paper-board. The inner and outer liner may be identical, or the outer layer may be preprinted or coated to better accept printing. The inner layer may be given a special coating to resist moisture. Heavy-duty shipping containers, such as corrugated bulk bins that are required to have high stacking strength, may have double- or even triple-wall construction. Corrugated fiberboard manufacturers print box certificates on the bottom of containers to certify certain strength characteristics and limitations. There are two types of certification. The first certifies the minimum combined weight of both the inner and outer facings and that the corrugated fiberboard material is of a minimum bursting strength. The second certifies minimum edge crush test (ETC) strength. Edge crush strength is a much better predictor of stacking strength than is bursting strength. For this reason, users of corrugated fiberboard containers should insist on ECT certification to compare the stackability of various containers. Both certificates give a maximum size limit for the container (sum of length, width, and height) and the maximum gross weight of the contents.
Both cold temperatures and high humidities reduce the strength of fiberboard containers. Unless the container is specially treated, moisture absorbed from the surrounding air and the contents can reduce the strength of the container by as much as 75 percent. New anti-moisture coatings (both wax and plastic) are now available to substantially reduce the effects of moisture.
Waxed fiberboard cartons (the wax is about 20 percent of fiber weight) are used for many produce items that must be either hydrocooled or iced. The main objection to wax cartons is disposal after use— wax cartons cannot be recycled and are increasingly being refused at landfills. Several states and municipalities have recently taxed wax cartons or have instituted rigid back haul regulations. Industry sources suggest that wax cartons will eventually be replaced by plastic or, more likely, the use of ice and hydrocooling will be replaced by highly controlled forced-air cooling and rigid temperature and humidity maintenance on many commodities.
In many applications for corrugated fiberboard containers, the stacking strength of the container is a minor consideration. For example, canned goods carry the majority of their own weight when stacked. Fresh produce usually cannot carry much of the vertical load without some damage.
Therefore, one of the primarily desired characteristics of corrugated fiberboard containers is stacking strength to protect the produce from crushing. Because of their geometry, most of the stacking strength of corrugated containers is carried by the corners. For this reason, hand holes and ventilation slots should never be positioned near the corners of produce containers and be limited to no more than 5 to 7 percent of the side area.
Interlocking the packages (cross stacking) is universally practiced to stabilize pallets. Cross stacking places the corner of one produce package at the middle of the one below it, thus reducing its stacking strength. To reduce the possibility of collapse, the first several layers of each pallet should be column stacked (one package directly above the other). The upper layers of packages may be cross stacked as usual with very little loss of pallet stability.
There are numerous styles of corrugated fiberboard containers. The two most used in the produce industry are the one piece, regular slotted container (RSC) and the two piece, full telescoping container (FTC). The RSC is the most popular because it is simple and economical. However, the RSC has relatively low stacking strength and therefore must be used with produce, such as potatoes, that can carry some of the stacking load. The FTC, actually one container inside another, is used when greater stack- ing strength and resistance to bulging is required. A third type of container is the Bliss box, which is — constructed from three separate pieces of corrugated fiberboard.
The Bliss box was developed to be used when maximum stacking strength is required. The bottoms and tops of all three types of containers may be closed by glue, staples, or interlocking slots.
Almost all corrugated fiberboard containers are shipped to the packer flat and assembled at the packing house. To conserve space, assembly is usually performed just before use. Assembly may be by hand, machine, or a combination of both. Ease of assembly should be carefully investigated when considering a particular style of package.
In recent years, large double-wall or even triple- wall corrugated fiberboard containers have increasingly been used as one-way pallet bins to ship bulk produce to processors and retailers. Cabbage, melons, potatoes, pumpkins, and citrus have all been shipped successfully in these containers. The container cost per pound of produce is as little as one fourth of traditional size containers. Some bulk containers may be collapsed and re-used.
For many years, labels were printed on heavy paper and glued or stapled to the produce package. The high cost of materials and labor has all but eliminated this practice. The ability to print the brand, size, and grade information directly on the container is one of the greatest benefits of corrugated fiberboard containers. There are basically two methods used to print corrugated fiberboard containers:
Post Printed. When the liner is printed after the corrugated fiberboard has been formed, the process is known as post printing. Post printing is the most widely used printing method for corrugated fiberboard containers because it is economical and may be used for small press runs. However, postprinting produces graphics with less detail and is usually limited to one or two colors.
Preprinted. High quality, full-color graphics may be obtained by preprinting the linerboard before it is attached to the corrugated paperboard. Whereas the cost is about 15 percent more than standard two color containers, the eye catching quality of the graphics makes it very useful for many situations. The visual quality of the package influences the perception of the product because the buyer's first impression is of the outside of the package. Produce managers especially like high quality graphics that they can use in super market floor displays.
Preprinted cartons are usually reserved for the introduction of new products or new brands. Market research has shown that exporters may benefit from sophisticated graphics. The increased cost usually does not justify use for mature products in a stable market, but this may change as the cost of these containers becomes more competitive.
Pulp Containers. Containers made from recycled paper pulp and a starch binder are mainly used for small consumer packages of fresh produce. Pulp containers are available in a large variety of shapes and sizes and are relatively inexpensive in standard sizes. Pulp containers can absorb surface moisture from the product, which is a benefit for small fruit and berries that are easily harmed by water. Pulp containers are also biodegradable, made from recycled materials, and recyclable.
Paper and Mesh Bags. Consumer packs of potatoes and onions are about the only produce items now packed in paper bags. The more sturdy mesh bag has much wider use. In addition to potatoes and onions, cabbage, turnips, citrus, and some specialty items are packed in mesh bags. Sweet corn may still be packaged in mesh bags in some markets. In addition to its low cost, mesh has the advantage of uninhibited air flow. Good ventilation is particularly beneficial to onions. Supermarket produce managers like small mesh bags because they make attractive displays that stimulate purchases.
However, bags of any type have several serious disadvantages. Large bags do not palletize well and small bags do not efficiently fill the space inside corrugated fiberboard containers. Bags do not offer protection from rough handling. Mesh bags provide little protection from light or contaminants. In addition, produce packed in bags is correctly perceived by the consumer to be less than the best grade. Few consumers are willing to pay premium price for bagged produce.
Plastic Bags. Plastic bags (polyethylene film) are the predominant material for fruit and vegetable consumer packaging. Besides the very low material costs, automated bagging machines further reduce packing costs. Film bags are clear, allowing for easy inspection of the contents, and readily accept high quality graphics. Plastic films are available in a wide range of thicknesses and grades and may be engineered to control the environmental gases inside the bag. The film material "breathes" at a rate necessary to maintain the correct mix of oxygen, carbon dioxide, and water vapor inside the bag. Since each produce item has its own unique requirement for environmental gases, modified atmosphere packaging material must be specially engineered for each item. Research has shown that the shelf life of fresh produce is extended considerably by this packaging. The explosive growth of precut produce is due in part to the availability of modified atmosphere packaging.
In addition to engineered plastic films, various patches and valves have been developed that affix to low-cost ordinary plastic film bags. These devices respond to temperature and control the mix of environmental gases.
Shrink Wrap. One of the newest trends in produce packaging is the shrink wrapping of individual produce items. Shrink wrapping has been used successfully to package potatoes, sweetpotatoes, apples, onions, sweet corn, cucumbers and a variety of tropical fruit. Shrink wrapping with an engineered plastic wrap can reduce shrinkage, protect the produce from disease, reduce mechanical damage and provide a good surface for stick-on labels.
Rigid Plastic Packages. packages with a top and bottom that are heat formed from one or two pieces of plastic are known as clamshells. Clamshells are gaining in popularity because they are inexpensive, versatile, provide excellent protection to the produce, and present a very pleasing consumer package. Clamshells are most often used with consumer packs of high value produce items like small fruit, berries, mushrooms, etc., or items that are easily damaged by crushing. Clamshells are used extensively with precut produce and prepared salads. Molded polystyrene and corrugated polystyrene containers have been test marketed as a substitute for waxed corrugated fiberboard. At present they are not generally cost competitive, but as environmental pressures grow, they may be more common. Heavy-molded polystyrene pallet bins have been adopted by a number of growers as a substitute for wooden pallet bins. Although at present their cost is over double that of wooden bins, they have a longer service life, are easier to clean, are recyclable, do not decay when wet, do not harbor disease, and may be nested and made collapsible.
As environmental pressures continue to grow, the disposal and recyclability of packaging material of all kinds will become a very important issue.
Common polyethylene may take from 200 to 400 years to breakdown in a landfill. The addition of 6 percent starch will reduce the time to 20 years or less. packaging material companies are developing starch-based polyethylene substitutes that will break down in a landfill as fast as ordinary paper.
The move to biodegradable or recyclable plastic packaging materials may be driven by cost in the long term, but by legislation in the near term. Some authorities have proposed a total ban on plastics. In this case, the supermarket of the early 21st century may resemble the grocery markets of the early 20th century.
Standardization of Packaging
Produce package standardization is interpreted differently by different groups. The wide variety of package sizes and material combinations is a result of the market responding to demands from many different segments of the produce industry. For example, many of the large-volume buyers of fresh produce are those most concerned with the environment. They demand less packaging and the use of more recyclable and biodegradable materials, yet would also like to have many different sizes of packages for convenience.
packers want to limit the variety of packages they must carry in stock, yet they have driven the trend toward preprinted, individualized containers.
Shippers and trucking companies want to standardize sizes so the packages may be better palletized and handled.
Produce buyers are not a homogeneous group. Buyers for grocery chains have different needs than buyers for food service. For grocery items normally sold in bulk, processors want largest size packages that they can handle efficiently - to minimize unpacking time and reduce the cost of handling or disposing of the used containers. Produce managers, on the other hand, want individualized, high quality graphics to entice retail buyers with in-store displays.
Selecting the right container for fresh produce is seldom a matter of personal choice for the packer. For each commodity, the market has unofficial, but nevertheless rigid standards for packaging; therefore it is very risky to use a nonstandard package. packaging technology, market acceptability, and disposal regulations are constantly changing. When choosing a package for fresh fruits and vegetables, packers must consult the market, and in some markets, standard packages may be required by law.
Packaging fresh fruits and vegetables is one of the more important steps in the long and complicated journey from grower to consumer. Bags, crates, hampers, baskets, cartons, bulk bins, and palletized containers are convenient containers for handling, transporting, and marketing fresh produce. More than 1,500 different types of packages are used for produce in the U.S. and the number continues to increase as the industry introduces new packaging materials and concepts. Although the industry generally agrees that container standardization is one way to reduce cost, the trend in recent years has moved toward a wider range of package sizes to accommodate the diverse needs of wholesalers, consumers, food service buyers, and processing operations.
Packing and packaging materials contribute a significant cost to the produce industry; therefore it is important that packers, shippers, buyers, and consumers have a clear understanding of the wide range of packaging options available. This fact sheet describes some of the many types of packaging, including their functions, uses, and limitations. Also included is a listing, by commodity, of the common produce containers standard to the industry.
The Function of Packaging or Why package Produce?
A significant percentage of produce buyer and consumer complaints may be traced to container failure because of poor design or inappropriate selection and use. A properly designed produce container should contain, protect, and identify the produce, satisfying everyone from grower to consumer.
PACKAGING POINTS
Recyclability/Biodegradability.
A growing number of U.S. markets and many export markets have waste disposal restrictions for packaging materials. In the near future, almost all produce packaging will be recyclable or biodegradable, or both. Many of the largest buyers of fresh produce are also those most concerned about environmental issues.
Variety.
The trend is toward greater use of bulk packages for processors and wholesale buyers and smaller packages for consumers. There are now more than 1,500 different sizes and styles of produce packages.
Sales Appeal.High quality graphics are increasingly being used to boost sales appeal. Multi-color printing, distinctive lettering, and logos are now common.
Shelf Life.
Modern produce packaging can be custom engineered for each commodity to extend shelf life and reduce waste.
Containment
The container must enclose the produce in convenient units for handling and distribution. The produce should fit well inside the container, with little wasted space. Small produce items that are spherical or oblong (such as potatoes, onions, and apples) may be packaged efficiently utilizing a variety of different package shapes and sizes. However, many produce items such as asparagus, berries, or soft fruit may require containers specially designed for that item.
packages of produce commonly handled by hand are usually limited to 50 pounds. Bulk packages moved by fork lifts may weigh as much as 1,200 pounds.
Protection
The package must protect the produce from mechanical damage and poor environmental conditions during handling and distribution. To produce buyers, torn, dented, or collapsed produce packages usually indicate lack of care in handling the contents. Produce containers must be sturdy enough to resist damage during packaging, storage, and transportation to market.
Because almost all produce packages are palletized, produce containers should have sufficient stacking strength to resist crushing in a low temperature, high humidity environment. Although the cost of packaging materials has escalated sharply in recent years, poor quality, lightweight containers that are easily damaged by handling or moisture are no longer tolerated by packers or buyers.
Produce destined for export markets requires that containers to be extra sturdy. Air-freighted produce may require special packing, package sizes, and insulation. Marketers who export fresh produce should consult with freight companies about any special packaging requirements. Additionally, the USDA and various state export agencies may be able to provide specific packaging information.
Damage resulting from poor environmental control during handling and transit is one of the leading causes of rejected produce and low buyer and consumer satisfaction. Each fresh fruit and vegetable commodity has its own requirements for temperature, humidity, and environmental gas composition.
Produce containers should be produce friendly - helping to maintain an optimum environment for the longest shelf life. This may include special materials to slow the loss of water from the produce, insulation materials to keep out the heat, or engineered plastic liners that maintain a favorable mix of oxygen and carbon dioxide.
Identification
The package must identify and provide useful information about the produce. It is customary (and may be required in some cases) to provide information such as the produce name, brand, size, grade, variety, net weight, count, grower, shipper, and country of origin. It is also becoming more common to find included on the package, nutritional information, recipes, and other useful information directed specifically at the consumer. In consumer marketing, pack- age appearance has also become an important part of point of sale displays.
Universal Product Codes (UPC or bar codes) may be included as part of the labeling. The UPCs used in the food industry consist of a ten-digit machine readable code. The first five digits are a number assigned to the specific producer (packer or shipper) and the second five digits represent specific product information such as type of produce and size of package. Although no price information is included, UPCs are used more and more by packers, shippers, buyers, and Example of a UPC retailers as a fast and convenient method of inventory control and cost accounting. Efficient use of UPCs requires coordination with everyone who handles the package.
Types of Packaging Materials
Wood
Pallets literally form the base on which most fresh produce is delivered to the consumer. Pallets were first used during World War II as an efficient way to move goods. The produce industry uses approximately 190 of the 700 million pallets produced per year in the U.S.. About 40 percent of these are single-use pallets. Because many are of a non-standard size, the pallets are built as inexpensively as possible and discarded after a single use. Although standardization efforts have been slowly under way for many years, the efforts have been accelerated by pressure from environmental groups, in addition to the rising cost of pallets and landfill tipping fees.
Over the years, the 40-inch wide, by 48-inch long pallet has evolved as the unofficial standard size. Standardization encourages re-use, which has many benefits. Besides reducing cost because they may be used many times, most pallet racks and automated pallet handling equipment are designed for standard-size pallets. Standard size pallets make efficient use of truck and van space and can accommodate heavier loads and more stress than lighter single-use pallets. Additionally, the use of a single pallet size could substantially reduce pallet inventory and warehousing costs along with pallet repair and disposal costs. The adoption of a pallet standard throughout the produce industry would also aid efforts toward standardization of produce containers.
In the early 1950s, an alternative to the pallet was introduced. It is a pallet-size sheet (slipsheet) of corrugated fiberboard or plastic (or a combination of these materials) with a narrow lip along one or more sides. packages of produce are stacked directly on this sheet as if it were a pallet. Once the packages are in place, they are moved by a specially equipped fork lift equipped with a thin metal sheet instead of forks.
Slipsheets are considerably less expensive than pallets to buy, store, and maintain; they may be re-used many times; and they reduce the tare weight of the load. However, they require the use of a special fork-lift attachment at each handling point from packer to retailer.
Depending on the size of produce package, a single pallet may carry from 20 to over 100 individual packages. Because these packages are often loosely stacked to allow for air circulation, or are bulging and difficult to stack evenly, they must be secured (unitized) to prevent shifting during handling and transit. Although widely used, plastic straps and tapes may not have completely satisfactory results. Plastic or paper corner tabs should always be used to prevent the straps from crushing the corners of packages.
Plastic stretch film is also widely used to secure produce packages. A good film must stretch, retain its elasticity, and cling to the packages. Plastic film may conform easily to various size loads. It helps protect the packages from loss of moisture, makes the pallet more secure against pilferage, and can be applied using partial automation. However, plastic film severely restricts proper ventilation. A common alternative to stretch film is plastic netting, which is much better for stabilizing some pallet loads, such as those that require forced-air cooling. Used stretch film and plastic netting may be difficult to properly handle and recycle.
A very low-cost and almost fully automated method of pallet stabilization is the application of a small amount of special glue to the top of each package.
As the packages are stacked, the glue secures all cartons together. This glue has a low tensile strength so cartons may be easily separated or repositioned, but a high shear strength so they will not slide. The glue does not present disposal or recycling problems.
Pallet Bins. Substantial wooden pallet bins of milled lumber or.plywood are primarily used to move produce from the field or orchard to the packing house. Depending on the application, capacities may range from 12 to more than 50 bushels. Although the height may vary, the length and width is generally the same as a standard pallet (48 inches by 40 inches). More efficient double-wide pallet bins (48 inches by 80 inches) are becoming more common in some produce operations.
Most pallet bins are locally made; therefore it is very important that they be consistent from lot to lot in materials, construction, and especially size. For example, small differences in overall dimensions Pallet bin can add up to big problems when several hundred are stacked together for cooling, ventilation, or storage. It is also important that stress points be adequately reinforced.
The average life of a hardwood pallet bin that is stored outside is approximately five years. When properly protected from the weather, pallets bins may have a useful life of 10 years or more.
Uniform voluntary standards for wood pallets and other wood containers are administered by the National Wooden Pallet and Container Association, Washington, DC. Additionally, the American Society of Agricultural Engineers, St. Joseph, Michigan, publishes standards for agricultural pallet bins (ASAE S337.1).
Wire-Bound Crates. Although alternatives are available, wooden wire-bound crates are used extensively for snap beans, sweet corn and several other commodities that require hydrocooling. Wire-bound crates are sturdy, rigid and have very high stacking strength that is essentially unaffected by water.
Wire-bound crates come in many different sizes from half- bushel to pallet-bin size and have a great deal of open space to facilitate cooling and ventilation. Although few are re-used, wire-bound crates may be dissembled after use and shipped back to the packer (flat). In some areas, used containers may pose a significant disposal problem. Wirebound crates are not generally acceptable for consumer packaging because of the difficulty in affixing suitable labels.
Wooden Crates and Lugs. Wooden crates, once extensively used for apples, stone fruit, and potatoes have been almost totally replaced by other types of containers. The relative expense of the container, a greater concern for tare weight, and advances in material handling have reduced their use to a few specialty items, such as expensive tropical fruit. The 15-, 20-, and 25-pound wooden lugs still used for bunch grapes and some specialty crops are being gradually replaced with less costly alternatives.
Wooden Baskets and Hampers. Wire-reinforced wood veneer baskets and hampers of different sizes were once used for a wide variety of crops from strawberries to sweetpotatoes. They are durable and may be nested for efficient transport when empty. However, cost, disposal problems, and difficulty in efficient palletization have severely limited their use to mostly local grower markets where they may be re-used many times.
Corrugated Fiberboard
Corrugated fiberboard (often mistakenly called cardboard or pasteboard) is manufactured in many different styles and weights. Because of its relativity low cost and versatility, it is the dominant produce container material and will probably remain so in the near future. The strength and serviceability of corrugated fiberboard have been improving in recent years.
Most corrugated fiberboard is made from three or more layers of paperboard manufactured by the kraft process. To be considered paperboard, the paper must be thicker than 0.008 inches. The grades of paperboard are differentiated by their weight (in pounds per 1,000 square feet) and their thickness. Kraft paper made from unbleached pulp has a characteristic brown color and is exceptionally strong. In addition to virgin wood fibers, Kraft paper may have some portion of synthetic fibers for additional strength, sizing (starch), and other materials to give it wet strength and printability.
Most fiberboard contains some recycled fibers. Minimum amounts of recycled materials may be specified by law and the percentage is expected to increase in the future. Tests have shown that cartons of fully recycled pulp have about 75 percent of the stacking strength of virgin fiber containers. The use of recycled fibers will inevitably lead to the use of thicker walled containers.
Double-faced corrugated fiberboard is the predominant form used for produce containers. It is produced by sandwiching a layer of corrugated paperboard between an inner and outer liner (facing) of paper-board. The inner and outer liner may be identical, or the outer layer may be preprinted or coated to better accept printing. The inner layer may be given a special coating to resist moisture. Heavy-duty shipping containers, such as corrugated bulk bins that are required to have high stacking strength, may have double- or even triple-wall construction. Corrugated fiberboard manufacturers print box certificates on the bottom of containers to certify certain strength characteristics and limitations. There are two types of certification. The first certifies the minimum combined weight of both the inner and outer facings and that the corrugated fiberboard material is of a minimum bursting strength. The second certifies minimum edge crush test (ETC) strength. Edge crush strength is a much better predictor of stacking strength than is bursting strength. For this reason, users of corrugated fiberboard containers should insist on ECT certification to compare the stackability of various containers. Both certificates give a maximum size limit for the container (sum of length, width, and height) and the maximum gross weight of the contents.
Both cold temperatures and high humidities reduce the strength of fiberboard containers. Unless the container is specially treated, moisture absorbed from the surrounding air and the contents can reduce the strength of the container by as much as 75 percent. New anti-moisture coatings (both wax and plastic) are now available to substantially reduce the effects of moisture.
Waxed fiberboard cartons (the wax is about 20 percent of fiber weight) are used for many produce items that must be either hydrocooled or iced. The main objection to wax cartons is disposal after use— wax cartons cannot be recycled and are increasingly being refused at landfills. Several states and municipalities have recently taxed wax cartons or have instituted rigid back haul regulations. Industry sources suggest that wax cartons will eventually be replaced by plastic or, more likely, the use of ice and hydrocooling will be replaced by highly controlled forced-air cooling and rigid temperature and humidity maintenance on many commodities.
In many applications for corrugated fiberboard containers, the stacking strength of the container is a minor consideration. For example, canned goods carry the majority of their own weight when stacked. Fresh produce usually cannot carry much of the vertical load without some damage.
Therefore, one of the primarily desired characteristics of corrugated fiberboard containers is stacking strength to protect the produce from crushing. Because of their geometry, most of the stacking strength of corrugated containers is carried by the corners. For this reason, hand holes and ventilation slots should never be positioned near the corners of produce containers and be limited to no more than 5 to 7 percent of the side area.
Interlocking the packages (cross stacking) is universally practiced to stabilize pallets. Cross stacking places the corner of one produce package at the middle of the one below it, thus reducing its stacking strength. To reduce the possibility of collapse, the first several layers of each pallet should be column stacked (one package directly above the other). The upper layers of packages may be cross stacked as usual with very little loss of pallet stability.
There are numerous styles of corrugated fiberboard containers. The two most used in the produce industry are the one piece, regular slotted container (RSC) and the two piece, full telescoping container (FTC). The RSC is the most popular because it is simple and economical. However, the RSC has relatively low stacking strength and therefore must be used with produce, such as potatoes, that can carry some of the stacking load. The FTC, actually one container inside another, is used when greater stack- ing strength and resistance to bulging is required. A third type of container is the Bliss box, which is — constructed from three separate pieces of corrugated fiberboard.
The Bliss box was developed to be used when maximum stacking strength is required. The bottoms and tops of all three types of containers may be closed by glue, staples, or interlocking slots.
Almost all corrugated fiberboard containers are shipped to the packer flat and assembled at the packing house. To conserve space, assembly is usually performed just before use. Assembly may be by hand, machine, or a combination of both. Ease of assembly should be carefully investigated when considering a particular style of package.
In recent years, large double-wall or even triple- wall corrugated fiberboard containers have increasingly been used as one-way pallet bins to ship bulk produce to processors and retailers. Cabbage, melons, potatoes, pumpkins, and citrus have all been shipped successfully in these containers. The container cost per pound of produce is as little as one fourth of traditional size containers. Some bulk containers may be collapsed and re-used.
For many years, labels were printed on heavy paper and glued or stapled to the produce package. The high cost of materials and labor has all but eliminated this practice. The ability to print the brand, size, and grade information directly on the container is one of the greatest benefits of corrugated fiberboard containers. There are basically two methods used to print corrugated fiberboard containers:
Post Printed. When the liner is printed after the corrugated fiberboard has been formed, the process is known as post printing. Post printing is the most widely used printing method for corrugated fiberboard containers because it is economical and may be used for small press runs. However, postprinting produces graphics with less detail and is usually limited to one or two colors.
Preprinted. High quality, full-color graphics may be obtained by preprinting the linerboard before it is attached to the corrugated paperboard. Whereas the cost is about 15 percent more than standard two color containers, the eye catching quality of the graphics makes it very useful for many situations. The visual quality of the package influences the perception of the product because the buyer's first impression is of the outside of the package. Produce managers especially like high quality graphics that they can use in super market floor displays.
Preprinted cartons are usually reserved for the introduction of new products or new brands. Market research has shown that exporters may benefit from sophisticated graphics. The increased cost usually does not justify use for mature products in a stable market, but this may change as the cost of these containers becomes more competitive.
Pulp Containers. Containers made from recycled paper pulp and a starch binder are mainly used for small consumer packages of fresh produce. Pulp containers are available in a large variety of shapes and sizes and are relatively inexpensive in standard sizes. Pulp containers can absorb surface moisture from the product, which is a benefit for small fruit and berries that are easily harmed by water. Pulp containers are also biodegradable, made from recycled materials, and recyclable.
Paper and Mesh Bags. Consumer packs of potatoes and onions are about the only produce items now packed in paper bags. The more sturdy mesh bag has much wider use. In addition to potatoes and onions, cabbage, turnips, citrus, and some specialty items are packed in mesh bags. Sweet corn may still be packaged in mesh bags in some markets. In addition to its low cost, mesh has the advantage of uninhibited air flow. Good ventilation is particularly beneficial to onions. Supermarket produce managers like small mesh bags because they make attractive displays that stimulate purchases.
However, bags of any type have several serious disadvantages. Large bags do not palletize well and small bags do not efficiently fill the space inside corrugated fiberboard containers. Bags do not offer protection from rough handling. Mesh bags provide little protection from light or contaminants. In addition, produce packed in bags is correctly perceived by the consumer to be less than the best grade. Few consumers are willing to pay premium price for bagged produce.
Plastic Bags. Plastic bags (polyethylene film) are the predominant material for fruit and vegetable consumer packaging. Besides the very low material costs, automated bagging machines further reduce packing costs. Film bags are clear, allowing for easy inspection of the contents, and readily accept high quality graphics. Plastic films are available in a wide range of thicknesses and grades and may be engineered to control the environmental gases inside the bag. The film material "breathes" at a rate necessary to maintain the correct mix of oxygen, carbon dioxide, and water vapor inside the bag. Since each produce item has its own unique requirement for environmental gases, modified atmosphere packaging material must be specially engineered for each item. Research has shown that the shelf life of fresh produce is extended considerably by this packaging. The explosive growth of precut produce is due in part to the availability of modified atmosphere packaging.
In addition to engineered plastic films, various patches and valves have been developed that affix to low-cost ordinary plastic film bags. These devices respond to temperature and control the mix of environmental gases.
Shrink Wrap. One of the newest trends in produce packaging is the shrink wrapping of individual produce items. Shrink wrapping has been used successfully to package potatoes, sweetpotatoes, apples, onions, sweet corn, cucumbers and a variety of tropical fruit. Shrink wrapping with an engineered plastic wrap can reduce shrinkage, protect the produce from disease, reduce mechanical damage and provide a good surface for stick-on labels.
Rigid Plastic Packages. packages with a top and bottom that are heat formed from one or two pieces of plastic are known as clamshells. Clamshells are gaining in popularity because they are inexpensive, versatile, provide excellent protection to the produce, and present a very pleasing consumer package. Clamshells are most often used with consumer packs of high value produce items like small fruit, berries, mushrooms, etc., or items that are easily damaged by crushing. Clamshells are used extensively with precut produce and prepared salads. Molded polystyrene and corrugated polystyrene containers have been test marketed as a substitute for waxed corrugated fiberboard. At present they are not generally cost competitive, but as environmental pressures grow, they may be more common. Heavy-molded polystyrene pallet bins have been adopted by a number of growers as a substitute for wooden pallet bins. Although at present their cost is over double that of wooden bins, they have a longer service life, are easier to clean, are recyclable, do not decay when wet, do not harbor disease, and may be nested and made collapsible.
As environmental pressures continue to grow, the disposal and recyclability of packaging material of all kinds will become a very important issue.
Common polyethylene may take from 200 to 400 years to breakdown in a landfill. The addition of 6 percent starch will reduce the time to 20 years or less. packaging material companies are developing starch-based polyethylene substitutes that will break down in a landfill as fast as ordinary paper.
The move to biodegradable or recyclable plastic packaging materials may be driven by cost in the long term, but by legislation in the near term. Some authorities have proposed a total ban on plastics. In this case, the supermarket of the early 21st century may resemble the grocery markets of the early 20th century.
Standardization of Packaging
Produce package standardization is interpreted differently by different groups. The wide variety of package sizes and material combinations is a result of the market responding to demands from many different segments of the produce industry. For example, many of the large-volume buyers of fresh produce are those most concerned with the environment. They demand less packaging and the use of more recyclable and biodegradable materials, yet would also like to have many different sizes of packages for convenience.
packers want to limit the variety of packages they must carry in stock, yet they have driven the trend toward preprinted, individualized containers.
Shippers and trucking companies want to standardize sizes so the packages may be better palletized and handled.
Produce buyers are not a homogeneous group. Buyers for grocery chains have different needs than buyers for food service. For grocery items normally sold in bulk, processors want largest size packages that they can handle efficiently - to minimize unpacking time and reduce the cost of handling or disposing of the used containers. Produce managers, on the other hand, want individualized, high quality graphics to entice retail buyers with in-store displays.
Selecting the right container for fresh produce is seldom a matter of personal choice for the packer. For each commodity, the market has unofficial, but nevertheless rigid standards for packaging; therefore it is very risky to use a nonstandard package. packaging technology, market acceptability, and disposal regulations are constantly changing. When choosing a package for fresh fruits and vegetables, packers must consult the market, and in some markets, standard packages may be required by law.
Friday, August 27, 2010
How Does A Refrigerator Work?
In the summertime, have you ever gotten out of a swimming pool and then felt very cold standing in the sun? That's because the water on your skin is evaporating. The air carries off the water vapor, and with it some of the heat is being taken away from your skin.
This is similar to what happens inside older refrigerators. Instead of water, though, the refrigerator uses chemicals to do the cooling.
There are two things that need to be known for refrigeration.
1. A gas cools on expansion.
2. When you have two things that are different temperatures that touch or are near each other, the hotter surface cools and the colder surface warms up. This is a law of physics called the Second Law of Thermodynamics.
Old Refrigerators
If you look at the back or bottom of an older refrigerator, you'll see a long thin tube that loops back and forth. This tube is connected to a pump, which is powered by an electric motor.
Inside the tube is Freon, a type of gas. Freon is the brand name of the gas. This gas, chemically is called Chloro-Flouro-Carbon or CFC. This gas was found to hurt the environment if it leaks from refrigerators. So now, other chemicals are used in a slightly different process (see next section below).
CFC starts out as a liquid. The pump pushes the CFC through a lot of coils in the freezer area. There the chemical turns to a vapor. When it does, it soaks up some of the heat that may be in the freezer compartment. As it does this, the coils get colder and the freezer begins to get colder.
In the regular part of your refrigerator, there are fewer coils and a larger space. So, less heat is soaked up by the coils and the CFC vapor.
The pump then sucks the CFC as a vapor and forces it through thinner pipes which are on the outside of the refrigerator. By compressing it, the CFC turns back into a liquid and heat is given off and is absorbed by the air around it. That's why it might be a little warmer behind or under your refrigerator.
Once the CFC passes through the outside coils, the liquid is ready to go back through the freezer and refrigerator over and over.
Today's Refrigerators
Modern refrigerators don't use CFC. Instead they use ammonia gas. Ammonia gas turns into a liquid when it is cooled to -27 degrees Fahrenheit (-6.5 degrees Celsius).
A motor and compressor squeezes the ammonia gas. When it is compressed, a gas heats up as it is pressurized. When you pass the compressed gas through the coils on the back or bottom of a modern refrigerator, the hot ammonia gas can lose its heat to the air in the room.
Remember the law of thermodynamics.
As it cools, the ammonia gas can change into ammonia liquid because it is under a high pressure.
The ammonia liquid flows through what's called an expansion valve, a tiny small hole that the liquid has to squeeze through. Between the valve and the compressor, there is a low-pressure area because the compressor is pulling the ammonia gas out of that side.
When the liquid ammonia hits a low pressure area it boils and changes into a gas. This is called vaporizing.
The coils then go through the freezer and regular part of the refrigerator where the colder ammonia in the coil pulls the heat out of the compartments. This makes the inside of the freezer and entire refrigerator cold.
The compressor sucks up the cold ammonia gas, and the gas goes back through the same process over and over.
How Does the Temperature Stay the Same Inside?
A device called a thermocouple (it's basically a thermometer) can sense when the temperature in the refrigerator is as cold as you want it to be. When it reaches that temperature, the device shuts off the electricity to the compressor.
But the refrigerator is not completely sealed. There are places, like around the doors and where the pipes go through, that can leak a little bit.
So when the cold from inside the refrigerator starts to leak out and the heat leaks in, the thermocouple turns the compressor back on to cool the refrigerator off again.
That's why you'll hear your refrigerator compressor motor coming on, running for a little while and then turning itself off.
Today's refrigerators, however, are very energy efficient. Ones sold today use about one-tenth the amount of electricity of ones that were built 20 years ago. So, if you have an old, old refrigerator, it's better to buy a new one because you'll save money (and energy) over a long period of time.
For more information go to:
• Argone National Laboratory - Ask A Scientist (http://newton.dep.anl.gov/newton/askasci/1993/eng/ENG30.HTM)
• Mr. Hand's 8th Grade Science Site (www.mansfieldct.org/schools/mms/staff/hand/heatrefrig.htm)
• How Stuff Works - Refrigerator (www.howstuffworks.com/refrigerator.htm)
• Science Treasure Trove - refrigerator page (www.education.eth.net/acads/treasure_trove/refrigerator.htm)
This is similar to what happens inside older refrigerators. Instead of water, though, the refrigerator uses chemicals to do the cooling.
There are two things that need to be known for refrigeration.
1. A gas cools on expansion.
2. When you have two things that are different temperatures that touch or are near each other, the hotter surface cools and the colder surface warms up. This is a law of physics called the Second Law of Thermodynamics.
Old Refrigerators
If you look at the back or bottom of an older refrigerator, you'll see a long thin tube that loops back and forth. This tube is connected to a pump, which is powered by an electric motor.
Inside the tube is Freon, a type of gas. Freon is the brand name of the gas. This gas, chemically is called Chloro-Flouro-Carbon or CFC. This gas was found to hurt the environment if it leaks from refrigerators. So now, other chemicals are used in a slightly different process (see next section below).
CFC starts out as a liquid. The pump pushes the CFC through a lot of coils in the freezer area. There the chemical turns to a vapor. When it does, it soaks up some of the heat that may be in the freezer compartment. As it does this, the coils get colder and the freezer begins to get colder.
In the regular part of your refrigerator, there are fewer coils and a larger space. So, less heat is soaked up by the coils and the CFC vapor.
The pump then sucks the CFC as a vapor and forces it through thinner pipes which are on the outside of the refrigerator. By compressing it, the CFC turns back into a liquid and heat is given off and is absorbed by the air around it. That's why it might be a little warmer behind or under your refrigerator.
Once the CFC passes through the outside coils, the liquid is ready to go back through the freezer and refrigerator over and over.
Today's Refrigerators
Modern refrigerators don't use CFC. Instead they use ammonia gas. Ammonia gas turns into a liquid when it is cooled to -27 degrees Fahrenheit (-6.5 degrees Celsius).
A motor and compressor squeezes the ammonia gas. When it is compressed, a gas heats up as it is pressurized. When you pass the compressed gas through the coils on the back or bottom of a modern refrigerator, the hot ammonia gas can lose its heat to the air in the room.
Remember the law of thermodynamics.
As it cools, the ammonia gas can change into ammonia liquid because it is under a high pressure.
The ammonia liquid flows through what's called an expansion valve, a tiny small hole that the liquid has to squeeze through. Between the valve and the compressor, there is a low-pressure area because the compressor is pulling the ammonia gas out of that side.
When the liquid ammonia hits a low pressure area it boils and changes into a gas. This is called vaporizing.
The coils then go through the freezer and regular part of the refrigerator where the colder ammonia in the coil pulls the heat out of the compartments. This makes the inside of the freezer and entire refrigerator cold.
The compressor sucks up the cold ammonia gas, and the gas goes back through the same process over and over.
How Does the Temperature Stay the Same Inside?
A device called a thermocouple (it's basically a thermometer) can sense when the temperature in the refrigerator is as cold as you want it to be. When it reaches that temperature, the device shuts off the electricity to the compressor.
But the refrigerator is not completely sealed. There are places, like around the doors and where the pipes go through, that can leak a little bit.
So when the cold from inside the refrigerator starts to leak out and the heat leaks in, the thermocouple turns the compressor back on to cool the refrigerator off again.
That's why you'll hear your refrigerator compressor motor coming on, running for a little while and then turning itself off.
Today's refrigerators, however, are very energy efficient. Ones sold today use about one-tenth the amount of electricity of ones that were built 20 years ago. So, if you have an old, old refrigerator, it's better to buy a new one because you'll save money (and energy) over a long period of time.
For more information go to:
• Argone National Laboratory - Ask A Scientist (http://newton.dep.anl.gov/newton/askasci/1993/eng/ENG30.HTM)
• Mr. Hand's 8th Grade Science Site (www.mansfieldct.org/schools/mms/staff/hand/heatrefrig.htm)
• How Stuff Works - Refrigerator (www.howstuffworks.com/refrigerator.htm)
• Science Treasure Trove - refrigerator page (www.education.eth.net/acads/treasure_trove/refrigerator.htm)
Tuesday, June 15, 2010
Enhance Marketing of Fruits and Vegetables
Fruits and vegetables are usually more difficult to market than to produce. There are ready markets available daily or weekly for grain and livestock in almost all areas of the United States. There are few similar markets for fruits and vegetables. Most commodities are produced in abundance and long established market channels may be closed to small scale or new producers. A producer may need several years to establish a marketing program. The number of produce buyers has decreased rapidly in recent years. One major nationwide supermarket chain has plans to consolidate the number of buying stations for produce to eight in the United States. A grower has little chance of selling to a local store in a supermarket chain as purchases are made through a central warehouse. As the number of buyers has decreased, the number of producers has decreased, but their acreage has increased considerably. There is often a delay of four to six months after shipment in receiving payment in the wholesale market system when selling through a broker. This often presents a cash flow problem for many growers. Wholesale buyers have strict and specific product quality, grade, and packaging requirements. These purchasing practices and price squeezes have eliminated market availability to many producers.
The future shows more promise for large scale producers or small scale producers than for mid sized producers. The large scale producer can afford the large equipment needed for production, and the use of migrant labor. Small scale producers can use smaller equipment, often hand operated, and family or local labor to substitute for other equipment. Large producers are linked through brokers to supply produce over a relatively long season or year round and it is difficult for small scale producers to supply the quantity and quality required over a long period. Both types of producers can be highly successful or can go broke as production and marketing practices are highly volatile. A mid sized producer is less efficient, and often can't economically justify the purchase of needed equipment or substitute labor for equipment.
The small scale producer needs to seek local market channels. There are opportunities, but a producer must work to find them. Direct to the consumer markets bring highest prices to the producer, but also require more producer time in marketing. A diverse group of crops is ideal, since market demand changes rapidly. A commodity may sell well and bring high prices for a long period, but demand and prices may drop drastically over night. Supply and demand has a tremendous effect on marketability and prices of produce. There are no federal support prices for fruits and vegetables to help the grower when market demand or prices drop. Pick-your-own was a popular practice a few years ago. Society has changed and many people do not have time for harvest. Most consumers would rather buy produce that is harvested, and a popular developing trend is to prepare produce for the market that is as near ready to eat as possible. Precut salads and green beans are good examples of this practice. Shelf life of precut produce is relatively short, and cooling is essential.
There are opportunities for small scale producers for on-farm markets, organized farm markets, locally owned supermarkets, and locally owned fruit and vegetable markets. When selling to any market, and especially to local supermarkets or fruit and vegetable markets, good communication between producer and buyer is essential. A producer needs to know what, when, and how much the buyer can use. The buyer needs to know what is available and when, as he has to keep the shelves stocked. Determining a fair price can be difficult. Daily market prices are available on the internet. County Extension personnel can access this information for producers. Retailers generally double the price paid to account for shrinkage and spoilage.
Crop and variety selection are critical factors in marketing. Buyers are indifferent to the origin of most crops. Locally grown produce is much preferred versus other crops, primarily due to the difference in quality (flavor). Preferences for locally grown fruit and vegetable crops are apparent for sweet corn, tomatoes, strawberries, and peaches. These commodities either are harvested for shipping before top quality is attained, or rapidly lose quality during post harvest handling and shipping.
Different varieties may be used in shipping markets as compared to local markets. The sweet corn shipping market uses mostly supersweet type varieties. Local markets may use supersweet type varieties, but usually prefer SE or SU type varieties. Certain crops or varieties are preferred in specific locations, and a ready local market may exist for a specific item that is not widely available.
A local Crossville, Tennessee market owner recently shared a list of items that he had difficulty in obtaining, and that he needed during the summer season. His list included Half Runner, McCaslan, Caseknife and Greasy beans; pickling cucumbers of 1.5 to 2 inch diameter; fresh highly flavored sweet corn (yellow, white and bicolor); Red Cayanne pepper; colored bell pepper; Kennebec and Yukon Gold potatoes; watermelons (seedy and seedless), strawberries; greenhouse tomatoes (fall, winter, and spring seasons); and highly flavored local tomatoes in the summer season. He had an idea for a tomato festival that included tomato varieties not routinely found in regular market channels. This would include Rutgers, Celebrity, cherry, beefsteak, pink, yellow, yellow and red striped, and pear shaped varieties. Many of these varieties are less productive and have other production problems, but have excellent flavor compared to the standard commercial hybrid varieties. There is a marketing opportunity through this market at Crossville, and similar situations probably exist in most locations in the United States. A producer needs to search for such market opportunities.
The budgets and profitability of crops is another factor in production. Tomatoes have consistently been the most profitable crop for Tennessee producers. Greenhouse production is completely different, but is a rapidly growing enterprise in Tennessee. Sweet corn can be profitable, especially if a high plant population is used to provide high yields. We are planting twice the population (23,500 plants/A) than was planted several years ago, and are evaluating spacings for higher populations. Budgets that detail costs of production and likely returns are available for most crops, or a grower can develop their own budget.
Tree fruit production does not fit well into small scale agricultural production. The time between planting a tree and the first economic fruit harvest is relatively long. Large equipment is necessary to apply pesticides 10 to 12 times annually starting at the first bud break. Many pesticides are restricted use, and require special handling procedures. Trees need to be pruned at planting and annually in late winter.
Grapes offer some opportunity, but strawberries and blueberries are small fruit that offer more opportunity for small scale producers. Large fruit are required for successful marketing of strawberries and blueberries. Drip irrigation is needed in most areas for stand establishment and crop production. Overhead sprinkler irrigation is often necessary for frost protection. Strawberry production systems are changing from matted row to annual production. The culture of each system is entirely different.
Harvest of fruit and vegetable crops at the proper maturity is essential. Many crops have a very narrow harvest window, and proper maturity is needed to insure a marketable product. Crops that producers tend to harvest early are sweet corn and bell pepper. Sweet corn that is not fully mature has less flavor, and little usable grain. Immature bell pepper pods wilt rapidly and are not attractive. Crops that can easily be harvested too late are sweet corn, bell pepper, and green beans. Bell pepper may be harvested with some color showing. Most markets want a green or colored pepper pod, and not a partially colored pod. Sweet corn and green beans become tough rapidly is allowed to become overmature. Tomatoes are best harvested in the pink stage and harvesting twice a week may be needed for proper maturity. Pink tomatoes have full flavor. Fruit rot, cracking, and bruising may be less when harvest is at the pink stage.
Packaging of produce is a critical factor in marketing. Containers should protect the product and be attractive. Standard packs vary according to the type of product and the market demand, but many buyers require the use of standard size containers. Some routine container sizes are half bushels, bushels, 1 + 1/9 bushel, standard sweet corn crates to hold 4 ½ dozen ears, and pints or quarts for berries. Many different types of materials are used in containers. Waxed pasteboard cartons are very widely used. Snap bean and sweet corn buyers often prefer wire bound wooden boxes. Melons are often sold in bulk cardboard boxes that hold approximately 250 muskmelon. Many markets may require specific counts and product size. for the container. Peppers and tomatoes are specific crops sold by uniform size. Peppers are usually boxed as extra large (40 to 50 -pods/1 + 1/9 bushel) to small (70 to 80 pods/1 + 1/9 bu box). This relatively uniform size allows the retail vendor to sell pepper pods by count. Prepacking in small consumer packages such as 3 potatoes or tomatoes is becoming more of a demand at the producer level. Local markets may have more or less stringent packaging requirements.
Product identification can be a useful tool in marketing. Certain areas or growers have developed a name for their product. Some examples are Vidalia onions, Granger County tomatoes, Washington apples, and Idaho potatoes. Product identification can work well for anyone who wants to stress and maintain quality. It should pay in repeat sales and prices received by the grower. We are considering this approach in Tennessee for Tri-X-Shadow seedless watermelon which has exceptional quality. An identification label could be attached to each melon citing the identification (maybe Tennessee Seedless).
Harvested fruits and vegetables are perishable, and quality loss starts immediately after harvest. Rapid marketing to insure freshness is a desirable feature of locally grown produce. Produce, not sold immediately, needs to be stored properly to maintain appearance, flavor, and quality. Time of harvest, cooling, and storing in shaded areas will help retain quality. Produce harvested early in the morning is cooler than if harvest is later in the day. Quality of products such as green beans, sweet corn, peppers, and peaches benefit from hydrocooling. Hydrocooled produce needs to be kept in a cooler to maintain the proper storage temperature after hydrocooling. Products such as broccoli and sweet corn benefit from storage with ice in the container or placed on ice to maintain a low temperature and to avoid drying of the produce. Produce that has been cooled, should be maintained in cool.
The future shows more promise for large scale producers or small scale producers than for mid sized producers. The large scale producer can afford the large equipment needed for production, and the use of migrant labor. Small scale producers can use smaller equipment, often hand operated, and family or local labor to substitute for other equipment. Large producers are linked through brokers to supply produce over a relatively long season or year round and it is difficult for small scale producers to supply the quantity and quality required over a long period. Both types of producers can be highly successful or can go broke as production and marketing practices are highly volatile. A mid sized producer is less efficient, and often can't economically justify the purchase of needed equipment or substitute labor for equipment.
The small scale producer needs to seek local market channels. There are opportunities, but a producer must work to find them. Direct to the consumer markets bring highest prices to the producer, but also require more producer time in marketing. A diverse group of crops is ideal, since market demand changes rapidly. A commodity may sell well and bring high prices for a long period, but demand and prices may drop drastically over night. Supply and demand has a tremendous effect on marketability and prices of produce. There are no federal support prices for fruits and vegetables to help the grower when market demand or prices drop. Pick-your-own was a popular practice a few years ago. Society has changed and many people do not have time for harvest. Most consumers would rather buy produce that is harvested, and a popular developing trend is to prepare produce for the market that is as near ready to eat as possible. Precut salads and green beans are good examples of this practice. Shelf life of precut produce is relatively short, and cooling is essential.
There are opportunities for small scale producers for on-farm markets, organized farm markets, locally owned supermarkets, and locally owned fruit and vegetable markets. When selling to any market, and especially to local supermarkets or fruit and vegetable markets, good communication between producer and buyer is essential. A producer needs to know what, when, and how much the buyer can use. The buyer needs to know what is available and when, as he has to keep the shelves stocked. Determining a fair price can be difficult. Daily market prices are available on the internet. County Extension personnel can access this information for producers. Retailers generally double the price paid to account for shrinkage and spoilage.
Crop and variety selection are critical factors in marketing. Buyers are indifferent to the origin of most crops. Locally grown produce is much preferred versus other crops, primarily due to the difference in quality (flavor). Preferences for locally grown fruit and vegetable crops are apparent for sweet corn, tomatoes, strawberries, and peaches. These commodities either are harvested for shipping before top quality is attained, or rapidly lose quality during post harvest handling and shipping.
Different varieties may be used in shipping markets as compared to local markets. The sweet corn shipping market uses mostly supersweet type varieties. Local markets may use supersweet type varieties, but usually prefer SE or SU type varieties. Certain crops or varieties are preferred in specific locations, and a ready local market may exist for a specific item that is not widely available.
A local Crossville, Tennessee market owner recently shared a list of items that he had difficulty in obtaining, and that he needed during the summer season. His list included Half Runner, McCaslan, Caseknife and Greasy beans; pickling cucumbers of 1.5 to 2 inch diameter; fresh highly flavored sweet corn (yellow, white and bicolor); Red Cayanne pepper; colored bell pepper; Kennebec and Yukon Gold potatoes; watermelons (seedy and seedless), strawberries; greenhouse tomatoes (fall, winter, and spring seasons); and highly flavored local tomatoes in the summer season. He had an idea for a tomato festival that included tomato varieties not routinely found in regular market channels. This would include Rutgers, Celebrity, cherry, beefsteak, pink, yellow, yellow and red striped, and pear shaped varieties. Many of these varieties are less productive and have other production problems, but have excellent flavor compared to the standard commercial hybrid varieties. There is a marketing opportunity through this market at Crossville, and similar situations probably exist in most locations in the United States. A producer needs to search for such market opportunities.
The budgets and profitability of crops is another factor in production. Tomatoes have consistently been the most profitable crop for Tennessee producers. Greenhouse production is completely different, but is a rapidly growing enterprise in Tennessee. Sweet corn can be profitable, especially if a high plant population is used to provide high yields. We are planting twice the population (23,500 plants/A) than was planted several years ago, and are evaluating spacings for higher populations. Budgets that detail costs of production and likely returns are available for most crops, or a grower can develop their own budget.
Tree fruit production does not fit well into small scale agricultural production. The time between planting a tree and the first economic fruit harvest is relatively long. Large equipment is necessary to apply pesticides 10 to 12 times annually starting at the first bud break. Many pesticides are restricted use, and require special handling procedures. Trees need to be pruned at planting and annually in late winter.
Grapes offer some opportunity, but strawberries and blueberries are small fruit that offer more opportunity for small scale producers. Large fruit are required for successful marketing of strawberries and blueberries. Drip irrigation is needed in most areas for stand establishment and crop production. Overhead sprinkler irrigation is often necessary for frost protection. Strawberry production systems are changing from matted row to annual production. The culture of each system is entirely different.
Harvest of fruit and vegetable crops at the proper maturity is essential. Many crops have a very narrow harvest window, and proper maturity is needed to insure a marketable product. Crops that producers tend to harvest early are sweet corn and bell pepper. Sweet corn that is not fully mature has less flavor, and little usable grain. Immature bell pepper pods wilt rapidly and are not attractive. Crops that can easily be harvested too late are sweet corn, bell pepper, and green beans. Bell pepper may be harvested with some color showing. Most markets want a green or colored pepper pod, and not a partially colored pod. Sweet corn and green beans become tough rapidly is allowed to become overmature. Tomatoes are best harvested in the pink stage and harvesting twice a week may be needed for proper maturity. Pink tomatoes have full flavor. Fruit rot, cracking, and bruising may be less when harvest is at the pink stage.
Packaging of produce is a critical factor in marketing. Containers should protect the product and be attractive. Standard packs vary according to the type of product and the market demand, but many buyers require the use of standard size containers. Some routine container sizes are half bushels, bushels, 1 + 1/9 bushel, standard sweet corn crates to hold 4 ½ dozen ears, and pints or quarts for berries. Many different types of materials are used in containers. Waxed pasteboard cartons are very widely used. Snap bean and sweet corn buyers often prefer wire bound wooden boxes. Melons are often sold in bulk cardboard boxes that hold approximately 250 muskmelon. Many markets may require specific counts and product size. for the container. Peppers and tomatoes are specific crops sold by uniform size. Peppers are usually boxed as extra large (40 to 50 -pods/1 + 1/9 bushel) to small (70 to 80 pods/1 + 1/9 bu box). This relatively uniform size allows the retail vendor to sell pepper pods by count. Prepacking in small consumer packages such as 3 potatoes or tomatoes is becoming more of a demand at the producer level. Local markets may have more or less stringent packaging requirements.
Product identification can be a useful tool in marketing. Certain areas or growers have developed a name for their product. Some examples are Vidalia onions, Granger County tomatoes, Washington apples, and Idaho potatoes. Product identification can work well for anyone who wants to stress and maintain quality. It should pay in repeat sales and prices received by the grower. We are considering this approach in Tennessee for Tri-X-Shadow seedless watermelon which has exceptional quality. An identification label could be attached to each melon citing the identification (maybe Tennessee Seedless).
Harvested fruits and vegetables are perishable, and quality loss starts immediately after harvest. Rapid marketing to insure freshness is a desirable feature of locally grown produce. Produce, not sold immediately, needs to be stored properly to maintain appearance, flavor, and quality. Time of harvest, cooling, and storing in shaded areas will help retain quality. Produce harvested early in the morning is cooler than if harvest is later in the day. Quality of products such as green beans, sweet corn, peppers, and peaches benefit from hydrocooling. Hydrocooled produce needs to be kept in a cooler to maintain the proper storage temperature after hydrocooling. Products such as broccoli and sweet corn benefit from storage with ice in the container or placed on ice to maintain a low temperature and to avoid drying of the produce. Produce that has been cooled, should be maintained in cool.
Thursday, April 1, 2010
Chain Management : Sounds Geekish, but is very much commonsense
Have you heard of Just-in-time, TQM, The rise of Toyota as a powerful global player in the automotive industry, even surpassing the gaping mouths of the big three in the United states? You would have certainly come across the term 'Supply Chain Management' - It sounds like jargon, doesn't it? Well, it isn't so difficult to understand and it is something most manufacturing ( even services!) industries indulge in today. Supply Chain management basically means that the process of managing the whole process of finding a suitable raw material, processing it and converting it into something valuable or useful that could be sold to the market.
The better a company is in managing its resources, the process of locating its raw materials, processing them, working on them, the entire production process, the out put, the packaging and even the labelling might constitute a simple supply chain management case study.
According to the CIO Magazine,
Supply chain management (SCM) is the combination of art and science that goes into improving the way your company finds the raw components it needs to make a product or service and deliver it to customers. The following are five basic components of SCM.
Supply Chain Management has a lot of visible and also invisible elements to it. The glamorous parts might probably be the vendor management and the like. It is the invisible parts of the supply chain that attain the status of primary importance. Things like labor management, procurement, warehouse management, Order processing, fulfillment and delivery.
The importance of supply chain management has been growing steadily over the recent years and more so because of the fact that the companies have been growing larger and larger in size.Due to this enormous increase in size, the companies gain more cost efficiency when they outsource some of the functions that they ought to do themselves to other specialized service companies that do the needful. This enables the larger companies to be more flexible, focus more on their core competencies and create more value for their customers, while retaining profits by reducing costs at the same time. The ubiquitous, simple to use, nature of the Internet has made it possible to automate some of its supply chain management elements with the help of robust supply chain management software ( Though it is always not so easy to do the implementation and execution part!).
The extended supply chain - the vendors and their vendors network, has always become a critical link in the new era of Modern supply management theory and has taken it to another realm where everything boils down to cost cutting such that the whole process can create value for the customer.
The better a company is in managing its resources, the process of locating its raw materials, processing them, working on them, the entire production process, the out put, the packaging and even the labelling might constitute a simple supply chain management case study.
According to the CIO Magazine,
Supply chain management (SCM) is the combination of art and science that goes into improving the way your company finds the raw components it needs to make a product or service and deliver it to customers. The following are five basic components of SCM.
Supply Chain Management has a lot of visible and also invisible elements to it. The glamorous parts might probably be the vendor management and the like. It is the invisible parts of the supply chain that attain the status of primary importance. Things like labor management, procurement, warehouse management, Order processing, fulfillment and delivery.
The importance of supply chain management has been growing steadily over the recent years and more so because of the fact that the companies have been growing larger and larger in size.Due to this enormous increase in size, the companies gain more cost efficiency when they outsource some of the functions that they ought to do themselves to other specialized service companies that do the needful. This enables the larger companies to be more flexible, focus more on their core competencies and create more value for their customers, while retaining profits by reducing costs at the same time. The ubiquitous, simple to use, nature of the Internet has made it possible to automate some of its supply chain management elements with the help of robust supply chain management software ( Though it is always not so easy to do the implementation and execution part!).
The extended supply chain - the vendors and their vendors network, has always become a critical link in the new era of Modern supply management theory and has taken it to another realm where everything boils down to cost cutting such that the whole process can create value for the customer.
Wednesday, March 31, 2010
Chain- A Way Forward
A consumer revolution is taking place in India as people change their eating habits and shopping patterns. While fresh foods have long been a staple, more people are putting a premium on speed and convenience. Supermarkets and shopping malls are cropping up everywhere, and sales of consumer-ready frozen foods are burgeoning, from ice cream and frozen entrees, to vegetables, fruits, sea foods and meats.
To meet this rising demand, manufactures and retailers of temperature sensitive products must move their perishable foods quickly, while emphasizing quality, safety, reliability, and traceability. This is a real challenge in a country where the cold-chain infrastructure still needs a lot of work to be done. India’s cold chain infrastructure is fragmented, under funded, and scrambling to keep up with soaring demand. The need of the hour is to address these concerns immediately.
The frozen food distribution is still not stabilized as most of the companies are still finding it difficult for service and are adopting the most rudimentary method of delivery of frozen/chilled foods to the trade. This, basically means that the integrity of the cold chain is being compromised. However, at this moment, the focus seems to be on survival and most of the companies are first interested in building volumes before they can provide high-class facilities for distribution of frozen/chilled products.
We at SNOWMAN, are now looking at expanding our network in terms of scale and reach if we are to compete at the domestic or international level. Our focus is to provide every requisite cold chain related solution to the customers but seeing the opportunity in F&V sector, definitely our focus would be more towards fruits and vegetables sector in the days to come along with new avenues like temperature controlled pharmaceutical products etc.
We are eagerly watching the prospects of large corporate like Reliance, Bharti, Aditya Birla Group, Mahindra & Mahindra , TATA and ITC etc to formulate and implement their retailing plan which will immensely benefit the cold chain industry. In my opinion, the cold chain industry will automatically grow as soon as the organized retail starts fully in place. All other difficulties will get resolved in due course of time. However basically what we need, is the consumer walking into a retail store and looking for chilled/frozen food products. This is the day when the cold chain industry will start moving forward and we have already seen the glimpse of it.
To meet this rising demand, manufactures and retailers of temperature sensitive products must move their perishable foods quickly, while emphasizing quality, safety, reliability, and traceability. This is a real challenge in a country where the cold-chain infrastructure still needs a lot of work to be done. India’s cold chain infrastructure is fragmented, under funded, and scrambling to keep up with soaring demand. The need of the hour is to address these concerns immediately.
The frozen food distribution is still not stabilized as most of the companies are still finding it difficult for service and are adopting the most rudimentary method of delivery of frozen/chilled foods to the trade. This, basically means that the integrity of the cold chain is being compromised. However, at this moment, the focus seems to be on survival and most of the companies are first interested in building volumes before they can provide high-class facilities for distribution of frozen/chilled products.
We at SNOWMAN, are now looking at expanding our network in terms of scale and reach if we are to compete at the domestic or international level. Our focus is to provide every requisite cold chain related solution to the customers but seeing the opportunity in F&V sector, definitely our focus would be more towards fruits and vegetables sector in the days to come along with new avenues like temperature controlled pharmaceutical products etc.
We are eagerly watching the prospects of large corporate like Reliance, Bharti, Aditya Birla Group, Mahindra & Mahindra , TATA and ITC etc to formulate and implement their retailing plan which will immensely benefit the cold chain industry. In my opinion, the cold chain industry will automatically grow as soon as the organized retail starts fully in place. All other difficulties will get resolved in due course of time. However basically what we need, is the consumer walking into a retail store and looking for chilled/frozen food products. This is the day when the cold chain industry will start moving forward and we have already seen the glimpse of it.
Friday, February 5, 2010
AMMONIA COMPRESSORS AND REFRIGERATION PLANT
INTRODUCTION
1 This circular gives advice on the precautions to be taken against the toxic, fire and explosion hazards presented by refrigeration systems containing ammonia. These are most likely to be found by LA enforcement officers at cold stores and food distribution warehouses. It applies to the entire system not simply the compressor house. It provides interim advice on matters of concern to enforcement officers pending revision of BS 4434:1980.
2 Appendix 1 outlines the general principles of refrigeration, Appendix 2 gives information on the results of the programme of special visits carried out in 1983 by Factory Inspectorate (F1) to examine present standards in the food industry and Appendix 3 gives detailed guidance on electrical standards. Enforcement officers should not overemphasise the hazards of ammonia compared with other refrigerants.
HAZARDS
Toxicity
3 Ammonia is a chemically reactive gas that is very soluble in water and is much lighter than air (vapour density 0.59 of that of air). Cold vapour (e.g. from leaks) may however be denser than air. Although there have been incidents of exposure to harmful concentrations of ammonia in the UK there have been few fatal accidents. Ammonia is characterised by a typical pungent odour and is detectable by most people at levels of about 50 ppm in the atmosphere. Although workers become tolerant to this effect and in the past have been able to work without distress at levels up to 70 ppm, currently the recommended exposure limit for ammonia is 25 ppm, 8 hour TWA (0.0025%) and the short term exposure limit is 35 ppm, 10 minute TWA. At 400 ppm, most people experience immediate nose and throat irritation, but suffer no permanent ill-effects after 30-60 minute exposure. A level of 700 ppm causes immediate irritation to the eyes, and a level of 1,700 ppm (0.17%) will give rise to repeated coughing and can be fatal after about 30 minutes exposure.
Exposure to concentrations exceeding 5,000 ppm (0.5%) for quite short periods can result in death. Response to the effects of ammonia varies widely between individuals, and the dose-response effects described above are likely to be those experienced by the more susceptible members of the population.
Fire and explosion
4 Ammonia forms a flammable mixture with air at concentrations between 16 and 25% v/v. There have however been very few incentive explosions involving ammonia compressor houses in the UK and all of the reported incidents involved ammonia leakage from plant under maintenance.
Existing guidance
5 Current guidance on the precautions which should be taken with ammonia refrigeration plant may be found in: British Standard 4434: 1980 "Requirements for Refrigeration Safety: Part 1, General". The requirements (particularly from the f ire and explosion standpoint) are similar to those in the earlier (1 969) version. However a' full revision of BS 4434 is taking place.
Precautions
6 Under normal circumstances people will not be able to bear ammonia concentrations at even a fraction of the flammable limit. The appropriate precautions are mainly those applicable against toxic effects in occupied areas and to work where sudden exposures are foreseeable, such as maintenance and repair work, including in particular filling and oil draining. Precautions against fire and explosion will be appropriate however, in unoccupied areas such as compressor houses and unattended plant such as cold stores where accumulations of vapour may go unnoticed.
PRECAUTIONS AGAINST TOXIC RISK
Respiratory protective equipment
7 Any person entering an area in which ammonia vapour is likely to be present at a significant level (eg for rescue or fault-finding purposes) must wear self-contained or airline breathing apparatus. This does not include routine visits to plant rooms etc. A suitable and properly maintained set should be conveniently sited close to, but outside, any area in which high levels of .ammonia vapour might arise. In no circumstances should anyone enter an area where a flammable concentration of gas may be present. Details of suitable apparatus are contained in Form 2501 "Certificate of Approval (Breathing Apparatus)," published annually by HSE. See also Guidance Note GS 5 regarding entry into confined spaces.
8 Suitable respiratory protective equipment must be worn by every person carrying out engineering maintenance work on any system where there is a risk of release of ammonia. Full face canister respirators with type A (blue) canisters give good protection in atmospheres up to 2% concentration or 20,000 ppm, for one hour. Work in such a concentration is likely to lead to discomfort quickly due to skin irritation as ammonia dissolves in perspiration.
A list of suitable equipment is given in form 2502 "Certificate of Approval (Canister Gas Respirators)". For substantial jobs impervious suits may be necessary if the gas cannot be cleared.
9 Everyone who is likely to need to use respiratory protective equipment must be properly trained in its use and must be fully aware of its limitations. The equipment must be maintained, kept clean and examined at least once a month. Appropriate records should be kept. If canister respirators are used there must be an effective system for deciding when the canisters should be renewed.
Evacuation and emergency procedures
10 lt is essential that a clear emergency procedure is drawn up which details the precise duties of all staff and the arrangements for evacuation, rescue, first aid, plant isolation etc. It is particularly important that evacuation procedures are clearly set out and regularly practised where refrigeration systems are in working areas. A common method which may be suitable is to use the fire alarm provided that actuating points are immediately available at working areas. Personnel should be warned not to approach any vapour clouds. (Clouds may often look like steam because of the cooling of the released gas).
11 Adequate exits should be maintained from plant rooms at, all times. Personnel seriously affected by an ammonia escape suffer streaming eyes and violent coughing and rapidly become disorientated. They therefore require clear prior knowledge of a safe exit route.
Training in plant operation and maintenance
12 All personnel involved in the operation and maintenance of the plant must be adequately trained. The training should cover not only general principles of refrigeration but also specific points related to the particular plant. This applies as much to maintenance contractors as to an employer's own staff.
PLANT LOCATION
Plant not designed for outdoor location
13 In the case of standard refrigeration plant (ie plant not specifically designed for outdoor location) exposure to excessively low air temperatures may cause liquefaction of ammonia within the compressor leading to compressor damage, which could be hazardous. This type of plant should therefore be sited in a compressor house using the precautions described in BS 4434:1980 and outlined below. Compressor-houses should, where reasonably practicable, be fitted with explosion relief (eg by using lightweight fragile roof). Where loosely held panels are used as explosion relief, they should be suitably restrained (eg by chains) to prevent them becoming dangerous missiles in the event of an explosion.
14 ln order to facilitate the provision of ventilation and explosion relief, compressor-houses should incorporate at least one external wall. The siting of compressors in confined areas, basements, etc should be avoided wherever practicable. Doors between plant rooms or compressor-houses and other parts of the building should be self-closing and well-fitting.
Plant designed for outdoor location
15 Only plant specifically designed for the conditions should be installed outdoors. Such installations should be sited in a safe position in the open air with, if necessary, weather protection using a Dutch barn type structure which has an evenly distributed minimum open area equivalent to at least 50% of the total wall area.
Plant in workrooms
16 As a general principle the amount of plant containing ammonia situated in workrooms and other populated areas should be minimised. Ancillary plant such as surge drums and liquid pumps should wherever possible be sited away from working areas. Compressors are often noisy and this is another reason for not having them in working areas.
Ventilation
17 Compress or houses should be provided with adequate and suitable ventilation to meet the following requirements:
(1) Normal Ventilation Sufficient permanent ventilation should be provided to prevent build up of toxic concentrations of ammonia from operational leakage (eg from seals, glands etc). It is probable that the redrafted British Standard will insist on mechanical car ventilation rather than rely on rather uncertain natural ventilation.
(2) Emergency ventilation Provision should be made for sufficient mechanical ventilation to prevent flammable ammonia/air mixtures accumulating in the event of reasonably foreseeable plant or operational failure (eg valve failure). In such circumstances the aim should be to keep concentrations below 25% of the lower explosive limit (ie 4%).
18 The ventilation requirements for a particular installation will depend on the type, capacity, operating conditions and location of the plant and may require individual assessment by a ventilation engineer with appropriate expertise. However, the following general points apply:
(1) permanent natural or mechanical ventilation, or a combination of both, may be used for normal or emergency ventilation. Mechanical ventilation initiated by gas detectors or manually (in the case of continuously manned plants) may also be used for emergency ventilation (see para 26); and Appendix 3 for electrical safety of the system;
(2) the ventilation should discharge to a safe place in the open air;
(3) in considering the ventilation to be provided, the potential effects of cold on plant should be taken into account (see para 12);
(4) flow of air through cracks around windows, doors etc, or the opening of windows or doors should not be relied on for ventilation;
(5) the formulae in BS4434 for quantifying ventilation requirements are rules of thumb based on unstated assumptions (eg they take no account of room size or leak rates). Inspectors should advise that the formulae may be used as a basic guide but discretion in their detailed application to a particular plant should be stressed. This is particularly important with very large systems when the ventilation required by the formulae becomes
impracticable; and
(6) it should be noted that the standard of ventilation given by the formulae in BS 4434: 1980 is not intended to deal with prolonged releases from major plant failure. However, the latter is very unlikely to occur in properly designed, constructed and maintained plant. Control of sources of ignition and plant shutdown (see paras 22-26) should also provide protection in such circumstances. Manually operated controls for emergency ventilation should be located in a safe, easily accessible place along with the control or switch for turning off the compressor.
Plant integrity
19 There can be serious corrosion of the low pressure. parts of pipework and plant due to condensation. It can progress unnoticed under lagging which is not effectively vapour sealed and is particularly rapid on plants which run intermittently and pass-through OoC. The general principles relating to the safety of pressure systems are appropriate. The system should be thoroughly examined by a competent person at regular intervals in accordance with a written scheme. There should be an effective maintenance scheme.
Pipework
20 All parts of refrigerating systems and in particular pipework should be positioned or protected to minimise the risk of impact damage, for example by fork lift trucks. Pipework and valves should be clearly marked to indicate their contents and function.
Oil drain system
21 Many of the reported incidents involving ammonia refrigeration systems have been the result of a malfunction of the oil drain system (designed to catch the "carry-over" of oil from the compressors). In most cases oil is drained from below liquid ammonia and is saturated with it. In addition the oil is viscous because it is cold. In order to minimise the risk of escape from this cause the following measures should be advised:
(1) where short distances are involved and adequate observation of the drain is possible oil drain pipes should terminate in a safe location in the open air. Valves on any pipe extension should not introduce the possibility of liquid ammonia being trapped; a bleed valve or hydrostatic relief valve venting to a safe place should be provided in the sections between valves, as appropriate;
(2) a double valve arrangement should be provided at oil drains. In addition to the operational manual valve, there should be an automatic closing spring or weight-loaded valve; and
(3) The use of oil drain catchpots. These are a useful feature on new plant, but existing plant cannot normally be easily modified. Before the oil is drained, the catchpot is isolated from the liquid ammonia/oil feedline and the catchpot is electrically heated to boil off any ammonia which flows as a vapour to the low pressure side of the system. When the catchpot is warm, it is also isolated on the vapour side and the oil is then drained from it.
Ammonia filling point
22 Ammonia filling points should be located in safe, well ventilated positions and, where reasonably practicable, in the open air. Filling points should be sited away from sources of ignition.
PRECAUTIONS AGAINST FIRE AND EXPLOSION RISK
Sources of ignition
23 All likely sources of ignition (naked flames etc) should be eliminated from compressor houses and from the immediate vicinity of externally located plant.
Electrical equipment
24 Guidance on electrical apparatus for use in potentially explosive atmospheres is given in RS 5345: Part 1: 1976 "Code of Practice for the Selection, Installation and Maintenance of Electrical Apparatus for Use in Potentially Explosive Atmospheres, Part 1, Basic Requirements for all Parts of the Code"; BS 4434: 1980, Clause 13 "Electrical Installations". The approaches followed by the above documents differ.
25 As a general principle, electrical equipment should be sited outside the compressor room in a safe location. However, when it is necessarily sited in the room, it should be in accordance with the guidance given in para 27.
26 Where the ammonia compressors and refrigeration plant are located in the same room as the supply switch gear for the-premises relocation would probably be inconvenient and costly. In such cases, Field Consultant Group (FCG) advise on the most suitable safety precautions in the particular case should be sought.
Electrical apparatus selection criteria
27 The use of electrical apparatus in refrigeration plants using ammonia has been considered a special case because of the flammability characteristics of the gas (high LEL and narrow explosive range) and the fact that it can be detected at very low levels by smell. This has resulted in a number of options which may be considered when selecting electrical apparatus for ammonia plants and these are considered in Appendix 3.
OTHER RISKS
28 Refrigeration systems often have associated risks which may require attention, These include the risk of trapping in cold stores and chills, the handling of very cold products and microbiological problems associated with cooling towers used for the condenser.
ENFORCEMENT APPROACH
29 Enforcement officers should advise that ammonia refrigeration plant should comply with the guidance in BS 4434: 1980 as amended and augmented by the information in this circular. They should however bear in mind:
(1) ammonia presents a toxic risk at concentrations far below those at which it presents any fire or explosion risk. There have been 2 gassing fatalities between 1977 and 1983 in the UK but only 3 incentive ammonia/air explosions in the last 20 years;
(2) the potential consequences of an incident in terms of injury to personnel, and the general public should be assessed;
(3) BS4434 was first published in 1969 and was not intended to be retrospective, although improvements in installations which pre-date the standard should be recommended, where reasonably practicable;
(4) analysis of the l983 visits strongly suggest that where poor conditions of the plant are found there is often inadequate attention to evacuation and emergency action; and
(5) where enforcement officers encounter maintenance contractors they should make enquiries about their working practices and training.
Further advice
30 This is a complicated technical subject and there are strong trade pressure groups. Enforcement officers are recommended to seek the advice of HSEs Field Consultant Group (FCG) via the Local Enforcement Liaison Officer (ELO), before considering enforcement action.
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Ammonia is used as a refrigerant because of particular thermodynamic properties which enable it to move heat far more efficiently than other refrigerant gases such as halogenated hydrocarbons. It is particularly suited to working in the range approximately OoC to -30oC and hence is widely used for food preservation, the chilling of liquids such as milk, beer and soft drinks, and in the chemical industry. New systems continue to be installed.
2. A simple system theoretically needs 4 components:
(1) evaporator;
(2) compressor;
(3) condenser; and
(4) reducing valve
In practice other components such as oil separator, intercooler, liquid receiver, surge drum and liquid pumps are often found.
3 The useful refrigeration is produced at the evaporator. Liquid ammonia at low pressure, and hence low temperature, takes in heat by vaporising. This vapour is removed by the compressor which, in compressing it, raises the temperature from below to above ambient. The hot compressed gas gives up the heat by condensing to a liquid in the condenser. The high pressure liquid then passes through the pressure reducing valve to the evaporator. At the valve the liquid is cooled as some vapour flashes off. The remaining liquid is available for use in the evaporator.
4 In a practical system it is likely there will be other items of plant. An oil separator removes suspended oil carried over from the compressor and either returns it to the (pressurised) crank-case or holds it for draining in some way. There may be a multi-stage compressor with an intercooler. This is cooled by bleeding high pressure liquid into the low pressure side.
Downstream of the condenser is generally a liquid receiver. Downstream of the reducing valve is often found a surge drum which acts as a reservoir of cold liquid and evens out demand on the compressor and condenser. The liquid ammonia is drawn from the surge drum by a pump. Oil drains may be found on surge drums, liquid receivers, and elsewhere on large plants. There is also likely to be an automatic control system on all but the oldest and smallest plants.
A simple practical refrigeration system
1 The aim was to collect information about a cross section of installations. One hundred and forty eight returns were used in the analysis which used the Edinburgh FCG microcomputer.
2 Returns covered a wide range of processes in the food and drinks industries. The largest single sector was dairying (chilled water supply) with substantial returns also from frozen food producers and cold stores. In the drinks sector cooling and soft drinks carbonators were the principal uses.
There were a wide range of other uses reported; most parts of the food industry require controlled temperatures below ambient at some part of their process. A wide range of sizes of installations from 45 kg to 45 tonne chargeweight were reported, 13% were over 5 tonnes, 40% between 1 and 5 tonnes, 35% between 100kg and 1 tonne and 12% 1 00 kg or below.
The oldest component reported was pre-war and there was a fairly even spread of age from 1960 to the present.
3 Eighty-nine per cent of installations had a separate compressor room. Forty-nine percent had the system charging point in the compressor room and 38% had it outdoors. Twenty-seven per cent of the sample could positively be identified as having doors to the outside of the building only. Thirty-six per cent of the other compressor rooms did not have self-closing doors and 17% did not have well-fitting doors. With compressors in a separate room this is a surprisingly large number where even the most rudimentary precautions to prevent the spread of escaping gas has not been taken. Fifty-five per cent had condensers mounted above ground level outside - typically on the roof.
This raises questions of safe access and also escape in the event of an emergency.
4 Thirty-six percent, had the evaporator in the workroom. (These were usually product freezers in the frozen food sector and carbonators at the soft drinks plants). This points to the need for effective emergency procedures in the event of leakage, particularly if it is in the workroom.
5 Only 3% of installations were identified as having pipework or plant capable of being damaged by, for example, fork lift trucks. Half of the entire survey however had unmarked pipework. (Notes of many proformas suggested that this would receive early attention).
6 lt proved impossible to carryout meaningful analysis of the ventilation provided in compressor rooms. A common installation seemed to rely largely on natural ventilation (perhaps assisted by a small fan) for normal ventilation. Where there was provision of ventilation specifically for emergencies, it tended to be a separate system rather than a 2 speed fan on the normal ventilating system. Only 23% of the installations had 2 ventilation rates available and only half the ventilation systems of any kind could be controlled from outside the compressor room. Only half of these ventilation systems were automatically controlled.
7 Only 16% of all system charging was done by a person on his own; the usual arrangement was 2 men. Oil draining was done by one man on his own at 30% of all Installations. At 51 % of all installations it was carried out more than once a month. Only 26% of installations had spring-loaded valves or a catchpot system at oil drains. Most of the rest had simply a short stub of pipe from a vessel containing liquid ammonia closed by a single valve. In 71 % of cases where the oil drain was unsatisfactory inspectors considered that the reasonably practicable improvement was the fitting of self-closing valves. The 30% of installations where one man did the oil draining on his own included 6 which had no respirator of any kind.
8 Forty-two per cent of compressor houses had no gas detectors. Sieger was by far the most common supplier (60%) of all detection systems. The most common service period of twice per year reflects that company's normal service contract. Nineteen per cent of detector systems were never checked.
Approximately half of the detector installations only had one operating level.
Twenty-seven per cent of systems did not shut down the plant but merely raised the alarm. Ten per cent of the systems had no separate alarm.
9 Sixty-six percent of compressor room electrical installations were not fully equipped to Zone 2 standard even where much of the plant was under the control of detectors. Seventy-five per cent of all compressor installations could be switched off elsewhere outside the compressor room (even if only at the main supply). Of the remainder, the main switchgear was either in the compressor room or access to it was through the compressor room.
10 Eighty-eight percent of all sites had 2 or more sets of respiratory protection of some kind. Six installations (4%) had none at all. At 83% of sites there was said to be some sort of training in the use of respiratory protection but only 43% had some sort of systematic examination. At only 5 installations (3.4%) were there possible limitations of space which conflicted with provision of respiratory protection and the main problem seemed to be access up ladders or around congested items of plant.
11 Forty-seven per cent of sites had reviving apparatus available usually for general first aid rather than specifically because of the ammonia.
12 Twenty-seven percent of sites had Draeger (or similar) detector tubes for measuring low concentrations of ammonia. Many others had sulphur sticks or hydrochloric acid for detecting small leaks.
13 Fifty-nine percent of installations were maintained at least partly by contractors. Apart from a few major suppliers and installers of equipment there were many local refrigeration engineers who only appeared once or twice in the survey. No information is available about the standard of training or workmanship of these contractors.
14 Fifty-five percent of all sites appeared to have emergency evacuation procedures (43% used the fire alarm) but slightly fewer (50%) appeared to give any training in these procedures. Only 24% appeared to have detailed rescue arrangements. Twenty-two per cent had written systems of work which appeared comprehensive and only 34% had what appeared to be effective plant operator training.
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APPENDIX 3 (paras 1 and 26)
PROTECTION OF ELECTRICAL APPARATUS AT AMMONIA COMPRESSORS AND REFRIGERATION PLANT
EXTERNALLY SITED PLANT
1 Compressors and refrigeration plant sited in out door locations in accordance with para 14 of this Circular in otherwise non-hazardous areas will not normally require specially protected electrical equipment.
INTERNALLY SITED PLANT
2 A flow chart of the basic requirements relating to the electrical apparatus for internally sited plant is given in the supplement to this appendix. The operational approaches are given below.
Option 1 - Use of explosion protected electrical apparatus
3 Hazardous area classification should be carried out by a competent person. Electrical apparatus should then be selected in accordance with BS 5345: Part 1: 1976 Section 2. The majority of compressor-houses should be regarded as Zone 2 areas. Type "N" explosion protected equipment (including any emergency ventilation fans) will be suitable for these locations.
Option 2 - Detection of leaks by personnel or gas detectors
4 ln this approach, non-explosion protected electrical apparatus, with qualifications, may be used in combination with a readily available means of isolating the electricity supply. The method of achieving the latter can be accomplished either automatically after detection of a leakage by a gas detector system, or manually after a leakage has been detected by personnel. The use of these techniques as a first line of defence is limited to applications solely involving ammonia in refrigeration plants. This approach is considered acceptable provided that the general principles outlined in paras 10-17 are followed and that sufficient account is taken of paras 5-9.
Gas detectors
5 The detectors should be suitably positioned taking into account the physical characteristics of the plant room, the pattern of airflow movement in it and the most likely sources of potential leakage. Due regard should be paid to any dead pockets or recesses. Experience has shown that, in certain circumstances, it is possible for cold ammonia vapour to stratify initially at low levels. Unless the occupier has adequate expertise within his own organisation, it would be advisable for him to consult a firm which specialises in the design and installation of gas detection systems.
6 As a rough guide only, one might expect to see detectors in the vicinity of the compressors and other non-static items of plant and at ceiling level where one detector per 36M2 of ceiling area would probably be sufficient, although more may be necessary if there are deep beams creating recesses. The objective is to ensure that the ammonia is detected and the apparatus rendered safe before flammable concentrations reach a source of ignition.
(This objective, which is also applicable to "detection" of a leak by personnel, is particularly critical with regard to electrical apparatus which is not specially designed to be non-sparking, non explosion-protected electrical apparatus and electrical apparatus with temperatures above 630'C).
7 The detectors should be suitably explosion protected.
8 The detectors used are of the "pellistor" type and may be subject to poisoning by airborne contaminants. They should therefore be properly installed and maintained and regularly checked. The operation of the detectors should be checked using standard ammonia gas mixtures. Certain V-belt dressings containing antimony have been shown to poison detectors and gradually reduce their response.
9 The detectors should be capable of detecting concentrations of ammonia at 1 % v/v or less.
Associated electrical apparatus
10 Account should be taken of the electrical control system circuitry and the maximum possible degree of failure to safety should be achieved, so far as is reasonably practicable. General guidance is contained in BS 5304:
1975 "Safeguarding of Machinery" Section 6.
11 The isolating device(s), whether manually or automatically operated, which cuts off the electricity supply to the ammonia plant room, should be located in a non-hazardous area. It can be either a contractor or circuit breaker. If the criteria in paras 5-9 above have been satisfied, the following recommendations in paras 13-17 should be adopted. (Although certain specific details have been taken from BS 4434:1980, by way of example, they are intended to indicate the general principles of this approach and not specific requirements -which will have, to be determined in each particular case).
12 Attention will need to be paid to the control of other circuits which enter the plant room and are not directly associated with the plant, eg socket outlets for portable tools.
Continuously manned rooms
13 Isolation of all electrical circuits should be effected by isolating devices located in a non-hazardous area. These devices should be controlled by push buttons immediately outside the plant room, or controlled by a gas detection system as described pare 14, and arranged to give visual and audible alarms to switch on equipment for emergency ventilation and/or emergency lighting (if installed). Any electrical apparatus that is required to operate in the room after a leakage has been detected, such as ventilation equipment and emergency lighting, should be suitably protected for the hazardous area in which it is sited, ie Zone 2. Few compressor rooms are continuously manned. Detection of leakage by operators is only reliable if they are continuously present in the room. If for example they have other duties, or leave the area for meals etc, or use an isolated noise refuge then the speed of response is likely to be substantially slower than that of automatic detectors.
Unmanned plant rooms
14 lsolation of all electrical circuits should be effected by isolating devices located in a non-hazardous area and controlled by one or more suitable ammonia gas detectors which should also be arranged to give a visual and audible alarm and to switch on equipment for ventilation and/or emergency lighting, if installed. The ventilation air should be discharged to the outside of the building in such a manner as not to cause distress or danger to persons in the vicinity of the building. Circuit isolation should be effected at ammonia concentrations below 25% LEL and an alarm setting of 1.5% v/v followed by circuit isolation at 3% v/v is suggested.
15 Maintenance personnel are required to enter unmanned plant rooms and adequate means of escape should be provided.
16 Personal protection including breathing apparatus, and possibly impervious suits, may be needed in any room or space if maintenance men are likely to dismantle pipework or do any other operation liable to release liquid ammonia or substantial quantities of gas.
Unmanned plant rooms linked to a continuously manned control room
17 ln certain applications, (eg chemical plant), sudden loss of cooling facilities caused by automatic shut-down of a refrigeration plant might possibly create a hazard. It is unlikely that this situation will ever arise in any premises in the JA sector of enforcement. In these circumstances isolation of the electrical equipment by manual intervention may be acceptable, provided that the detector/alarm system is directly linked to a continuously manned control room. Other actions initiated by the detector such as the operation of emergency ventilation may still be feasible. Acceptance of this procedure, when automatic plant shut-down has been shown to be not reasonably practicable, will also require that:
(1) the alarm arrangement and monitoring of the alarms (ie the manning of the control rooms) is satisfactory;
(2) suitable isolation facilities for the compressor and unprotected electrical equipment are available in a safe place; and
(3) as a safe system of work is provided for entry into the compressor room and for the overall assessment of the potential hazard and any other necessary action (eg plant isolation). (see paras 6-8 of this circular for personal protection).
1 This circular gives advice on the precautions to be taken against the toxic, fire and explosion hazards presented by refrigeration systems containing ammonia. These are most likely to be found by LA enforcement officers at cold stores and food distribution warehouses. It applies to the entire system not simply the compressor house. It provides interim advice on matters of concern to enforcement officers pending revision of BS 4434:1980.
2 Appendix 1 outlines the general principles of refrigeration, Appendix 2 gives information on the results of the programme of special visits carried out in 1983 by Factory Inspectorate (F1) to examine present standards in the food industry and Appendix 3 gives detailed guidance on electrical standards. Enforcement officers should not overemphasise the hazards of ammonia compared with other refrigerants.
HAZARDS
Toxicity
3 Ammonia is a chemically reactive gas that is very soluble in water and is much lighter than air (vapour density 0.59 of that of air). Cold vapour (e.g. from leaks) may however be denser than air. Although there have been incidents of exposure to harmful concentrations of ammonia in the UK there have been few fatal accidents. Ammonia is characterised by a typical pungent odour and is detectable by most people at levels of about 50 ppm in the atmosphere. Although workers become tolerant to this effect and in the past have been able to work without distress at levels up to 70 ppm, currently the recommended exposure limit for ammonia is 25 ppm, 8 hour TWA (0.0025%) and the short term exposure limit is 35 ppm, 10 minute TWA. At 400 ppm, most people experience immediate nose and throat irritation, but suffer no permanent ill-effects after 30-60 minute exposure. A level of 700 ppm causes immediate irritation to the eyes, and a level of 1,700 ppm (0.17%) will give rise to repeated coughing and can be fatal after about 30 minutes exposure.
Exposure to concentrations exceeding 5,000 ppm (0.5%) for quite short periods can result in death. Response to the effects of ammonia varies widely between individuals, and the dose-response effects described above are likely to be those experienced by the more susceptible members of the population.
Fire and explosion
4 Ammonia forms a flammable mixture with air at concentrations between 16 and 25% v/v. There have however been very few incentive explosions involving ammonia compressor houses in the UK and all of the reported incidents involved ammonia leakage from plant under maintenance.
Existing guidance
5 Current guidance on the precautions which should be taken with ammonia refrigeration plant may be found in: British Standard 4434: 1980 "Requirements for Refrigeration Safety: Part 1, General". The requirements (particularly from the f ire and explosion standpoint) are similar to those in the earlier (1 969) version. However a' full revision of BS 4434 is taking place.
Precautions
6 Under normal circumstances people will not be able to bear ammonia concentrations at even a fraction of the flammable limit. The appropriate precautions are mainly those applicable against toxic effects in occupied areas and to work where sudden exposures are foreseeable, such as maintenance and repair work, including in particular filling and oil draining. Precautions against fire and explosion will be appropriate however, in unoccupied areas such as compressor houses and unattended plant such as cold stores where accumulations of vapour may go unnoticed.
PRECAUTIONS AGAINST TOXIC RISK
Respiratory protective equipment
7 Any person entering an area in which ammonia vapour is likely to be present at a significant level (eg for rescue or fault-finding purposes) must wear self-contained or airline breathing apparatus. This does not include routine visits to plant rooms etc. A suitable and properly maintained set should be conveniently sited close to, but outside, any area in which high levels of .ammonia vapour might arise. In no circumstances should anyone enter an area where a flammable concentration of gas may be present. Details of suitable apparatus are contained in Form 2501 "Certificate of Approval (Breathing Apparatus)," published annually by HSE. See also Guidance Note GS 5 regarding entry into confined spaces.
8 Suitable respiratory protective equipment must be worn by every person carrying out engineering maintenance work on any system where there is a risk of release of ammonia. Full face canister respirators with type A (blue) canisters give good protection in atmospheres up to 2% concentration or 20,000 ppm, for one hour. Work in such a concentration is likely to lead to discomfort quickly due to skin irritation as ammonia dissolves in perspiration.
A list of suitable equipment is given in form 2502 "Certificate of Approval (Canister Gas Respirators)". For substantial jobs impervious suits may be necessary if the gas cannot be cleared.
9 Everyone who is likely to need to use respiratory protective equipment must be properly trained in its use and must be fully aware of its limitations. The equipment must be maintained, kept clean and examined at least once a month. Appropriate records should be kept. If canister respirators are used there must be an effective system for deciding when the canisters should be renewed.
Evacuation and emergency procedures
10 lt is essential that a clear emergency procedure is drawn up which details the precise duties of all staff and the arrangements for evacuation, rescue, first aid, plant isolation etc. It is particularly important that evacuation procedures are clearly set out and regularly practised where refrigeration systems are in working areas. A common method which may be suitable is to use the fire alarm provided that actuating points are immediately available at working areas. Personnel should be warned not to approach any vapour clouds. (Clouds may often look like steam because of the cooling of the released gas).
11 Adequate exits should be maintained from plant rooms at, all times. Personnel seriously affected by an ammonia escape suffer streaming eyes and violent coughing and rapidly become disorientated. They therefore require clear prior knowledge of a safe exit route.
Training in plant operation and maintenance
12 All personnel involved in the operation and maintenance of the plant must be adequately trained. The training should cover not only general principles of refrigeration but also specific points related to the particular plant. This applies as much to maintenance contractors as to an employer's own staff.
PLANT LOCATION
Plant not designed for outdoor location
13 In the case of standard refrigeration plant (ie plant not specifically designed for outdoor location) exposure to excessively low air temperatures may cause liquefaction of ammonia within the compressor leading to compressor damage, which could be hazardous. This type of plant should therefore be sited in a compressor house using the precautions described in BS 4434:1980 and outlined below. Compressor-houses should, where reasonably practicable, be fitted with explosion relief (eg by using lightweight fragile roof). Where loosely held panels are used as explosion relief, they should be suitably restrained (eg by chains) to prevent them becoming dangerous missiles in the event of an explosion.
14 ln order to facilitate the provision of ventilation and explosion relief, compressor-houses should incorporate at least one external wall. The siting of compressors in confined areas, basements, etc should be avoided wherever practicable. Doors between plant rooms or compressor-houses and other parts of the building should be self-closing and well-fitting.
Plant designed for outdoor location
15 Only plant specifically designed for the conditions should be installed outdoors. Such installations should be sited in a safe position in the open air with, if necessary, weather protection using a Dutch barn type structure which has an evenly distributed minimum open area equivalent to at least 50% of the total wall area.
Plant in workrooms
16 As a general principle the amount of plant containing ammonia situated in workrooms and other populated areas should be minimised. Ancillary plant such as surge drums and liquid pumps should wherever possible be sited away from working areas. Compressors are often noisy and this is another reason for not having them in working areas.
Ventilation
17 Compress or houses should be provided with adequate and suitable ventilation to meet the following requirements:
(1) Normal Ventilation Sufficient permanent ventilation should be provided to prevent build up of toxic concentrations of ammonia from operational leakage (eg from seals, glands etc). It is probable that the redrafted British Standard will insist on mechanical car ventilation rather than rely on rather uncertain natural ventilation.
(2) Emergency ventilation Provision should be made for sufficient mechanical ventilation to prevent flammable ammonia/air mixtures accumulating in the event of reasonably foreseeable plant or operational failure (eg valve failure). In such circumstances the aim should be to keep concentrations below 25% of the lower explosive limit (ie 4%).
18 The ventilation requirements for a particular installation will depend on the type, capacity, operating conditions and location of the plant and may require individual assessment by a ventilation engineer with appropriate expertise. However, the following general points apply:
(1) permanent natural or mechanical ventilation, or a combination of both, may be used for normal or emergency ventilation. Mechanical ventilation initiated by gas detectors or manually (in the case of continuously manned plants) may also be used for emergency ventilation (see para 26); and Appendix 3 for electrical safety of the system;
(2) the ventilation should discharge to a safe place in the open air;
(3) in considering the ventilation to be provided, the potential effects of cold on plant should be taken into account (see para 12);
(4) flow of air through cracks around windows, doors etc, or the opening of windows or doors should not be relied on for ventilation;
(5) the formulae in BS4434 for quantifying ventilation requirements are rules of thumb based on unstated assumptions (eg they take no account of room size or leak rates). Inspectors should advise that the formulae may be used as a basic guide but discretion in their detailed application to a particular plant should be stressed. This is particularly important with very large systems when the ventilation required by the formulae becomes
impracticable; and
(6) it should be noted that the standard of ventilation given by the formulae in BS 4434: 1980 is not intended to deal with prolonged releases from major plant failure. However, the latter is very unlikely to occur in properly designed, constructed and maintained plant. Control of sources of ignition and plant shutdown (see paras 22-26) should also provide protection in such circumstances. Manually operated controls for emergency ventilation should be located in a safe, easily accessible place along with the control or switch for turning off the compressor.
Plant integrity
19 There can be serious corrosion of the low pressure. parts of pipework and plant due to condensation. It can progress unnoticed under lagging which is not effectively vapour sealed and is particularly rapid on plants which run intermittently and pass-through OoC. The general principles relating to the safety of pressure systems are appropriate. The system should be thoroughly examined by a competent person at regular intervals in accordance with a written scheme. There should be an effective maintenance scheme.
Pipework
20 All parts of refrigerating systems and in particular pipework should be positioned or protected to minimise the risk of impact damage, for example by fork lift trucks. Pipework and valves should be clearly marked to indicate their contents and function.
Oil drain system
21 Many of the reported incidents involving ammonia refrigeration systems have been the result of a malfunction of the oil drain system (designed to catch the "carry-over" of oil from the compressors). In most cases oil is drained from below liquid ammonia and is saturated with it. In addition the oil is viscous because it is cold. In order to minimise the risk of escape from this cause the following measures should be advised:
(1) where short distances are involved and adequate observation of the drain is possible oil drain pipes should terminate in a safe location in the open air. Valves on any pipe extension should not introduce the possibility of liquid ammonia being trapped; a bleed valve or hydrostatic relief valve venting to a safe place should be provided in the sections between valves, as appropriate;
(2) a double valve arrangement should be provided at oil drains. In addition to the operational manual valve, there should be an automatic closing spring or weight-loaded valve; and
(3) The use of oil drain catchpots. These are a useful feature on new plant, but existing plant cannot normally be easily modified. Before the oil is drained, the catchpot is isolated from the liquid ammonia/oil feedline and the catchpot is electrically heated to boil off any ammonia which flows as a vapour to the low pressure side of the system. When the catchpot is warm, it is also isolated on the vapour side and the oil is then drained from it.
Ammonia filling point
22 Ammonia filling points should be located in safe, well ventilated positions and, where reasonably practicable, in the open air. Filling points should be sited away from sources of ignition.
PRECAUTIONS AGAINST FIRE AND EXPLOSION RISK
Sources of ignition
23 All likely sources of ignition (naked flames etc) should be eliminated from compressor houses and from the immediate vicinity of externally located plant.
Electrical equipment
24 Guidance on electrical apparatus for use in potentially explosive atmospheres is given in RS 5345: Part 1: 1976 "Code of Practice for the Selection, Installation and Maintenance of Electrical Apparatus for Use in Potentially Explosive Atmospheres, Part 1, Basic Requirements for all Parts of the Code"; BS 4434: 1980, Clause 13 "Electrical Installations". The approaches followed by the above documents differ.
25 As a general principle, electrical equipment should be sited outside the compressor room in a safe location. However, when it is necessarily sited in the room, it should be in accordance with the guidance given in para 27.
26 Where the ammonia compressors and refrigeration plant are located in the same room as the supply switch gear for the-premises relocation would probably be inconvenient and costly. In such cases, Field Consultant Group (FCG) advise on the most suitable safety precautions in the particular case should be sought.
Electrical apparatus selection criteria
27 The use of electrical apparatus in refrigeration plants using ammonia has been considered a special case because of the flammability characteristics of the gas (high LEL and narrow explosive range) and the fact that it can be detected at very low levels by smell. This has resulted in a number of options which may be considered when selecting electrical apparatus for ammonia plants and these are considered in Appendix 3.
OTHER RISKS
28 Refrigeration systems often have associated risks which may require attention, These include the risk of trapping in cold stores and chills, the handling of very cold products and microbiological problems associated with cooling towers used for the condenser.
ENFORCEMENT APPROACH
29 Enforcement officers should advise that ammonia refrigeration plant should comply with the guidance in BS 4434: 1980 as amended and augmented by the information in this circular. They should however bear in mind:
(1) ammonia presents a toxic risk at concentrations far below those at which it presents any fire or explosion risk. There have been 2 gassing fatalities between 1977 and 1983 in the UK but only 3 incentive ammonia/air explosions in the last 20 years;
(2) the potential consequences of an incident in terms of injury to personnel, and the general public should be assessed;
(3) BS4434 was first published in 1969 and was not intended to be retrospective, although improvements in installations which pre-date the standard should be recommended, where reasonably practicable;
(4) analysis of the l983 visits strongly suggest that where poor conditions of the plant are found there is often inadequate attention to evacuation and emergency action; and
(5) where enforcement officers encounter maintenance contractors they should make enquiries about their working practices and training.
Further advice
30 This is a complicated technical subject and there are strong trade pressure groups. Enforcement officers are recommended to seek the advice of HSEs Field Consultant Group (FCG) via the Local Enforcement Liaison Officer (ELO), before considering enforcement action.
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Ammonia is used as a refrigerant because of particular thermodynamic properties which enable it to move heat far more efficiently than other refrigerant gases such as halogenated hydrocarbons. It is particularly suited to working in the range approximately OoC to -30oC and hence is widely used for food preservation, the chilling of liquids such as milk, beer and soft drinks, and in the chemical industry. New systems continue to be installed.
2. A simple system theoretically needs 4 components:
(1) evaporator;
(2) compressor;
(3) condenser; and
(4) reducing valve
In practice other components such as oil separator, intercooler, liquid receiver, surge drum and liquid pumps are often found.
3 The useful refrigeration is produced at the evaporator. Liquid ammonia at low pressure, and hence low temperature, takes in heat by vaporising. This vapour is removed by the compressor which, in compressing it, raises the temperature from below to above ambient. The hot compressed gas gives up the heat by condensing to a liquid in the condenser. The high pressure liquid then passes through the pressure reducing valve to the evaporator. At the valve the liquid is cooled as some vapour flashes off. The remaining liquid is available for use in the evaporator.
4 In a practical system it is likely there will be other items of plant. An oil separator removes suspended oil carried over from the compressor and either returns it to the (pressurised) crank-case or holds it for draining in some way. There may be a multi-stage compressor with an intercooler. This is cooled by bleeding high pressure liquid into the low pressure side.
Downstream of the condenser is generally a liquid receiver. Downstream of the reducing valve is often found a surge drum which acts as a reservoir of cold liquid and evens out demand on the compressor and condenser. The liquid ammonia is drawn from the surge drum by a pump. Oil drains may be found on surge drums, liquid receivers, and elsewhere on large plants. There is also likely to be an automatic control system on all but the oldest and smallest plants.
A simple practical refrigeration system
1 The aim was to collect information about a cross section of installations. One hundred and forty eight returns were used in the analysis which used the Edinburgh FCG microcomputer.
2 Returns covered a wide range of processes in the food and drinks industries. The largest single sector was dairying (chilled water supply) with substantial returns also from frozen food producers and cold stores. In the drinks sector cooling and soft drinks carbonators were the principal uses.
There were a wide range of other uses reported; most parts of the food industry require controlled temperatures below ambient at some part of their process. A wide range of sizes of installations from 45 kg to 45 tonne chargeweight were reported, 13% were over 5 tonnes, 40% between 1 and 5 tonnes, 35% between 100kg and 1 tonne and 12% 1 00 kg or below.
The oldest component reported was pre-war and there was a fairly even spread of age from 1960 to the present.
3 Eighty-nine per cent of installations had a separate compressor room. Forty-nine percent had the system charging point in the compressor room and 38% had it outdoors. Twenty-seven per cent of the sample could positively be identified as having doors to the outside of the building only. Thirty-six per cent of the other compressor rooms did not have self-closing doors and 17% did not have well-fitting doors. With compressors in a separate room this is a surprisingly large number where even the most rudimentary precautions to prevent the spread of escaping gas has not been taken. Fifty-five per cent had condensers mounted above ground level outside - typically on the roof.
This raises questions of safe access and also escape in the event of an emergency.
4 Thirty-six percent, had the evaporator in the workroom. (These were usually product freezers in the frozen food sector and carbonators at the soft drinks plants). This points to the need for effective emergency procedures in the event of leakage, particularly if it is in the workroom.
5 Only 3% of installations were identified as having pipework or plant capable of being damaged by, for example, fork lift trucks. Half of the entire survey however had unmarked pipework. (Notes of many proformas suggested that this would receive early attention).
6 lt proved impossible to carryout meaningful analysis of the ventilation provided in compressor rooms. A common installation seemed to rely largely on natural ventilation (perhaps assisted by a small fan) for normal ventilation. Where there was provision of ventilation specifically for emergencies, it tended to be a separate system rather than a 2 speed fan on the normal ventilating system. Only 23% of the installations had 2 ventilation rates available and only half the ventilation systems of any kind could be controlled from outside the compressor room. Only half of these ventilation systems were automatically controlled.
7 Only 16% of all system charging was done by a person on his own; the usual arrangement was 2 men. Oil draining was done by one man on his own at 30% of all Installations. At 51 % of all installations it was carried out more than once a month. Only 26% of installations had spring-loaded valves or a catchpot system at oil drains. Most of the rest had simply a short stub of pipe from a vessel containing liquid ammonia closed by a single valve. In 71 % of cases where the oil drain was unsatisfactory inspectors considered that the reasonably practicable improvement was the fitting of self-closing valves. The 30% of installations where one man did the oil draining on his own included 6 which had no respirator of any kind.
8 Forty-two per cent of compressor houses had no gas detectors. Sieger was by far the most common supplier (60%) of all detection systems. The most common service period of twice per year reflects that company's normal service contract. Nineteen per cent of detector systems were never checked.
Approximately half of the detector installations only had one operating level.
Twenty-seven per cent of systems did not shut down the plant but merely raised the alarm. Ten per cent of the systems had no separate alarm.
9 Sixty-six percent of compressor room electrical installations were not fully equipped to Zone 2 standard even where much of the plant was under the control of detectors. Seventy-five per cent of all compressor installations could be switched off elsewhere outside the compressor room (even if only at the main supply). Of the remainder, the main switchgear was either in the compressor room or access to it was through the compressor room.
10 Eighty-eight percent of all sites had 2 or more sets of respiratory protection of some kind. Six installations (4%) had none at all. At 83% of sites there was said to be some sort of training in the use of respiratory protection but only 43% had some sort of systematic examination. At only 5 installations (3.4%) were there possible limitations of space which conflicted with provision of respiratory protection and the main problem seemed to be access up ladders or around congested items of plant.
11 Forty-seven per cent of sites had reviving apparatus available usually for general first aid rather than specifically because of the ammonia.
12 Twenty-seven percent of sites had Draeger (or similar) detector tubes for measuring low concentrations of ammonia. Many others had sulphur sticks or hydrochloric acid for detecting small leaks.
13 Fifty-nine percent of installations were maintained at least partly by contractors. Apart from a few major suppliers and installers of equipment there were many local refrigeration engineers who only appeared once or twice in the survey. No information is available about the standard of training or workmanship of these contractors.
14 Fifty-five percent of all sites appeared to have emergency evacuation procedures (43% used the fire alarm) but slightly fewer (50%) appeared to give any training in these procedures. Only 24% appeared to have detailed rescue arrangements. Twenty-two per cent had written systems of work which appeared comprehensive and only 34% had what appeared to be effective plant operator training.
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APPENDIX 3 (paras 1 and 26)
PROTECTION OF ELECTRICAL APPARATUS AT AMMONIA COMPRESSORS AND REFRIGERATION PLANT
EXTERNALLY SITED PLANT
1 Compressors and refrigeration plant sited in out door locations in accordance with para 14 of this Circular in otherwise non-hazardous areas will not normally require specially protected electrical equipment.
INTERNALLY SITED PLANT
2 A flow chart of the basic requirements relating to the electrical apparatus for internally sited plant is given in the supplement to this appendix. The operational approaches are given below.
Option 1 - Use of explosion protected electrical apparatus
3 Hazardous area classification should be carried out by a competent person. Electrical apparatus should then be selected in accordance with BS 5345: Part 1: 1976 Section 2. The majority of compressor-houses should be regarded as Zone 2 areas. Type "N" explosion protected equipment (including any emergency ventilation fans) will be suitable for these locations.
Option 2 - Detection of leaks by personnel or gas detectors
4 ln this approach, non-explosion protected electrical apparatus, with qualifications, may be used in combination with a readily available means of isolating the electricity supply. The method of achieving the latter can be accomplished either automatically after detection of a leakage by a gas detector system, or manually after a leakage has been detected by personnel. The use of these techniques as a first line of defence is limited to applications solely involving ammonia in refrigeration plants. This approach is considered acceptable provided that the general principles outlined in paras 10-17 are followed and that sufficient account is taken of paras 5-9.
Gas detectors
5 The detectors should be suitably positioned taking into account the physical characteristics of the plant room, the pattern of airflow movement in it and the most likely sources of potential leakage. Due regard should be paid to any dead pockets or recesses. Experience has shown that, in certain circumstances, it is possible for cold ammonia vapour to stratify initially at low levels. Unless the occupier has adequate expertise within his own organisation, it would be advisable for him to consult a firm which specialises in the design and installation of gas detection systems.
6 As a rough guide only, one might expect to see detectors in the vicinity of the compressors and other non-static items of plant and at ceiling level where one detector per 36M2 of ceiling area would probably be sufficient, although more may be necessary if there are deep beams creating recesses. The objective is to ensure that the ammonia is detected and the apparatus rendered safe before flammable concentrations reach a source of ignition.
(This objective, which is also applicable to "detection" of a leak by personnel, is particularly critical with regard to electrical apparatus which is not specially designed to be non-sparking, non explosion-protected electrical apparatus and electrical apparatus with temperatures above 630'C).
7 The detectors should be suitably explosion protected.
8 The detectors used are of the "pellistor" type and may be subject to poisoning by airborne contaminants. They should therefore be properly installed and maintained and regularly checked. The operation of the detectors should be checked using standard ammonia gas mixtures. Certain V-belt dressings containing antimony have been shown to poison detectors and gradually reduce their response.
9 The detectors should be capable of detecting concentrations of ammonia at 1 % v/v or less.
Associated electrical apparatus
10 Account should be taken of the electrical control system circuitry and the maximum possible degree of failure to safety should be achieved, so far as is reasonably practicable. General guidance is contained in BS 5304:
1975 "Safeguarding of Machinery" Section 6.
11 The isolating device(s), whether manually or automatically operated, which cuts off the electricity supply to the ammonia plant room, should be located in a non-hazardous area. It can be either a contractor or circuit breaker. If the criteria in paras 5-9 above have been satisfied, the following recommendations in paras 13-17 should be adopted. (Although certain specific details have been taken from BS 4434:1980, by way of example, they are intended to indicate the general principles of this approach and not specific requirements -which will have, to be determined in each particular case).
12 Attention will need to be paid to the control of other circuits which enter the plant room and are not directly associated with the plant, eg socket outlets for portable tools.
Continuously manned rooms
13 Isolation of all electrical circuits should be effected by isolating devices located in a non-hazardous area. These devices should be controlled by push buttons immediately outside the plant room, or controlled by a gas detection system as described pare 14, and arranged to give visual and audible alarms to switch on equipment for emergency ventilation and/or emergency lighting (if installed). Any electrical apparatus that is required to operate in the room after a leakage has been detected, such as ventilation equipment and emergency lighting, should be suitably protected for the hazardous area in which it is sited, ie Zone 2. Few compressor rooms are continuously manned. Detection of leakage by operators is only reliable if they are continuously present in the room. If for example they have other duties, or leave the area for meals etc, or use an isolated noise refuge then the speed of response is likely to be substantially slower than that of automatic detectors.
Unmanned plant rooms
14 lsolation of all electrical circuits should be effected by isolating devices located in a non-hazardous area and controlled by one or more suitable ammonia gas detectors which should also be arranged to give a visual and audible alarm and to switch on equipment for ventilation and/or emergency lighting, if installed. The ventilation air should be discharged to the outside of the building in such a manner as not to cause distress or danger to persons in the vicinity of the building. Circuit isolation should be effected at ammonia concentrations below 25% LEL and an alarm setting of 1.5% v/v followed by circuit isolation at 3% v/v is suggested.
15 Maintenance personnel are required to enter unmanned plant rooms and adequate means of escape should be provided.
16 Personal protection including breathing apparatus, and possibly impervious suits, may be needed in any room or space if maintenance men are likely to dismantle pipework or do any other operation liable to release liquid ammonia or substantial quantities of gas.
Unmanned plant rooms linked to a continuously manned control room
17 ln certain applications, (eg chemical plant), sudden loss of cooling facilities caused by automatic shut-down of a refrigeration plant might possibly create a hazard. It is unlikely that this situation will ever arise in any premises in the JA sector of enforcement. In these circumstances isolation of the electrical equipment by manual intervention may be acceptable, provided that the detector/alarm system is directly linked to a continuously manned control room. Other actions initiated by the detector such as the operation of emergency ventilation may still be feasible. Acceptance of this procedure, when automatic plant shut-down has been shown to be not reasonably practicable, will also require that:
(1) the alarm arrangement and monitoring of the alarms (ie the manning of the control rooms) is satisfactory;
(2) suitable isolation facilities for the compressor and unprotected electrical equipment are available in a safe place; and
(3) as a safe system of work is provided for entry into the compressor room and for the overall assessment of the potential hazard and any other necessary action (eg plant isolation). (see paras 6-8 of this circular for personal protection).
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