| | Storage Systems | Handling Systems
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Storage Systems
Storage systems provide a stable, controlled environment that minimizes deterioration of the fresh produce. These systems can also be adapted to curing and pre-cooling. See Series 6000 plans from Canada Plan Service on the Internet at http://www.cps.gov.on.ca/ for storage systems.
If the storage facilities are to be used for rapid pre-cooling, the capacity of the refrigeration system must be increased. The amount of increase will be determined by the rate of harvest, the desired cooling time and the required temperature drop. The specific heat of fresh produce is about 0.85 BTUs per pound per degree Fahrenheit. For example, if the harvest rate is 1000 pounds per hour, and the cooling is to be done in 0.5 hour and the temperature drop is 40 degrees Fahrenheit, then the system will require an extra 1000 X 40 X 0.85 / 0.5 = 68000 BTUs per hour. Consider ice to be a source of refrigeration. It can dramatically reduce the size of the refrigeration system required by spreading the extra refrigeration load (required for making ice) out over a long period.
Handling Systems
Handling systems must be appropriate, not only for the produce, but also for the pre-cooling, storage, shipping and marketing systems. Handling systems do not add value to the product, but they do have a major effect on the maintenance of produce quality and the cost of post-harvest operations.
The potential for system scale up should also be considered so that the process can be done with minimal changes to the basic system. Equipment and containers used for handling should be easily cleaned and sanitized.
Containers used in handling systems must accommodate the type of cooling to be used as well as the harvesting, handling and shipping operations. In some cases, the containers are used at the retail level as well. Containers require at least 15 per cent open area for the air to enter and 15 per cent open area for the outlet located opposite the inlet. If the containers are to be stacked, the outlets must line up with the inlets to permit air to flow through the stack. Other openings in the containers can result in air bypassing the produce if the flow is not restricted.
Machine-harvested root crops are generally handled in bulk from the field. After washing and grading, these crops may be handled with pallet systems. Corn and some squash may also be handled in bulk from the field.
Green produce and fruit are generally handled with pallet systems from field to market. Some very small operations may use individual containers.
As with all handling systems, the actual handling of produce should be kept to a minimum. If produce can be packed into market-ready containers in the field and immediately pre-cooled, the handling costs can be minimized. In addition, deterioration resulting from holding non-pre-cooled produce, as well as contamination and bruising, can all be kept to a minimum. Market gardeners may find that the additional costs of harvest operations, to accommodate pre-cooling and to reduce contamination and bruising, can be balanced out against the resulting lower handling and produce deterioration costs.
Handling of produce can be done in bulk, in pallet bins and pallets of boxes, trays, baskets, trays of baskets, porous sacks and pails.
Bulk systems can be the cause of considerable damage to the produce if the systems are not carefully designed and operated. Loading and unloading equipment should lower produce as gently as possible to avoid bruising and should avoid exposing the produce to sharp edges. Also, be aware of pressure damage due to produce piled to excessive depths.
Bulk systems are very cost effective if damage to the produce can be minimized. Bulk handling systems can also readily accommodate expansion, again, if damage to the produce is minimized.
Pallet-based systems are very versatile and expandable. They can be used in handling, curing, pre-cooling, storage and shipping systems from field to market. Pallet bins can be stacked high without causing pressure damage to the produce. Different lots of produce can also be kept separate for effective inventory control. Because of these benefits, pallets are the preferred way of handling the wide range of market garden produce.
Pallet bins can be used as an integral part of harvest operations for transport, curing, pre-cooling and storage. In some instances, pallet bins of produce can be shipped directly to market.
Pallet bins used for produce curing and pre-cooling must have perforations. It is best to have slotted holes in only the bottoms of the pallets. This configuration will accommodate vertical forced air, hydro-cooling and ice based pre-cooling systems. Also, natural convection is better accommodated with slot-type perforations in the pallet bottom.
Palletized containers of produce can be handled and managed in a way similar to pallet bins. Totes, trays or cases of produce can be stacked on the pallets in the field. If the produce is to be cooled with forced air, the containers and pallets must have openings that line up when the containers are stacked on the pallets. This alignment is to permit the air to be forced through each of the containers and thus around all the produce.
For vertical flow systems, both the bottom and top of the containers should have at least 15 per cent of the area open. It is much better to have 30 per cent openings if the strength of the containers is not seriously compromised. For horizontal flow systems, opposite sides of the containers should each have 15 per cent openings. Forced air pre-cooling can be done in the field to minimize the time from harvest to cooling, thus optimizing the effects of pre-cooling.
Individual container handling systems are generally only appropriate for very small operations. Cases, totes, sacks, pails and baskets can be used in harvest, handling, shipping and marketing operations. They can be handled individually or with the aid of a hand cart.
If these containers are to be used in cooling systems, they must have at least 15 per cent of the bottoms open to allow for air flow and/or drainage. As with palletized systems used with forced air cooling, individual containers must permit the flow of air from one container to the next if forced air cooling is to be effective. Containers used for cooling berries should have slotted holes instead of round ones to minimize air blockage by the berries.
- open-top totes and containers
If open-top totes or containers are to be used in a forced-air cooling system, the top of one tote or container needs to seal against the bottom of the one above it.
If this configuration is not feasible, a "mask" (see Figure 9) can be used. A mask is a sheet of material with openings that sits on top of a row of totes or containers. The openings are located over the totes or containers in such a way so that air travels around the produce to chill it. The next row of totes or containers is then stacked, so they are centred over these openings in the mask. This structure forces the chilled air to pass through the containers and not around them. |
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