Although the practice of icing is decreasing for many of the same reasons as hydrocooling, crushed or liquid icing may be used effectively for a limited variety of fresh produce. Direct contact with ice is not recommended for produce that cannot tolerate wetting, might be injured by the ice particles, or could be damaged by chilling such as peppers or squash. Market acceptance may also influence icing’s use as a postharvest cooling method. In the past, buyers have demanded that cartons of broccoli arrive with visible ice as an indicator of proper postharvest cooling. It is permissible to top ice precooled reefers of sweet corn and other produce by blowing crushed ice over the top after loading. Top icing has the added benefit of keeping some items like leafy greens crisp and fresh. In addition to wetting the produce and requiring waterproof containers, icing is also heavy and adds to the shipping weight. Shipping companies are often reluctant to allow top icing because the icing wets the plywood interiors of their reefers.

For many small to moderate volume growers and producers of short-season fruits and vegetables, icing may provide a more economical cooling option because of the relatively small capital outlay. Ice was widely available at one time in 300 lb blocks. However, blocks of ice have become almost impossible to find and can be rather expensive during the peak of the harvest season. Growers who plan to use block ice should secure reliable sources well before harvest, and for food safety, should protect the crushed ice from contamination at all times.

In some cases, it may be advantageous for a small grower to install a small flake icemaker. These ice makers may be positioned conveniently in or near a small, insulated room and allowed to operate continually to produce substantial quantities of ice. The ice may be used as needed. Unless the ice is used on a regular basis, however, the flakes will freeze together into a solid mass that makes it extremely difficult to handle.

The simplest icing method involves adding a measured amount of crushed ice manually to the top of each carton filled with produce, which is a process known as package or top icing. The ice melts and cools the produce as the extra ice helps to maintain the cooling. Top icing is often automated as shown in Figure 3c-1. A general rule is to use about two lb of ice for each two or three lb of produce. Since melting ice wets the produce and package, waxed cartons, wire bound crates, or some of the newer plastic cartons will be required.

A quicker technology, liquid icing, has been used with great success on a number of crops, particularly broccoli and asparagus. Liquid icing is a hybrid of package icing and hydrocooling. In the simplest form, a mixture of water and finely crushed ice is pumped into open containers as they move along a conveyor as shown in Figure 3c-2. This method is a significant improvement over manual top icing because water carries the ice into the spaces in the package, which brings the ice into greater contact with the produce. With produce that has been field packed into cartons and palletized, the slurry may be pumped into the hand openings of each container. This method is very fast and effective and does not require the packages to be opened or un-palletized.

A faster, more automatic method for liquid icing of palletized produce is shown in Figure 3c-3. A pallet of filled cartons is placed inside a metal enclosure that is filled rapidly with a slurry of water and ice. The water and ice penetrate all spaces in the cartons. After the enclosure is filled, the excess slurry is drained, which leaves the ice inside the cartons. An automatic pallet icing operation such as the one in Figure 3c-3 can be controlled by the lift truck operator.

Figure 3c-1. An automated package icing line.

Source: NC State University.

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Figure 3c-1. An automated package icing line.

Source: NC State University.

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Figure 3c-2. Injecting liquid ice into palletized broccoli cartons through the hand openings.

Source: NC State University.

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Figure 3c-2. Injecting liquid ice into palletized broccoli cartons through the hand openings.

Source: NC State University.

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Figure 3c-3. Automated pallet ice system.

Photo: M. Boyette.

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Figure 3c-3. Automated pallet ice system.

Photo: M. Boyette.

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Those who use ice for cooling fresh produce must be aware of food safety issues. Ice is always 32°F or below, and can contain dangerous pathogens. Many outbreaks of norovirus and other gastrointestinal illnesses have been traced to contaminated ice. It is incorrect to assume that ice will be safe if the source of water is safe. With proper handling or mishandling, ice can become contaminated. Therefore, ice or the water from melting ice should be treated as if it were a food product. Since ice comes into contact with produce that may be eaten raw, cooking is not a safeguard. Thus, surfaces, containers, and tools that handle ice should be handled, cleaned, and stored in the same way as any item that comes in contact with food.