Cooling of Food Products

the lowering of the temperature of vegetable and animal food products to slow or partially arrest the life activity of microorganisms that cause spoilage. The cooling of food products also lowers enzyme activity, which leads to undesirable qualitative changes in the products. The procedure constitutes an independent process or a preliminary stage for the freezing of food products. Usually products that are cooled are those whose internal physiological processes still continue; an example of such a process is the respiration of fruits and vegetables. In such cases, the temperature is brought to a level at which the activity of microflora and enzymes is at a minimum.

The temperature for cooling food products should be above the freezing temperature in order to avoid crystallization of water in the cells and disruption of the normal structure of the products. Fruits and vegetables are usually cooled at temperatures from – 1° to – 1.2°C. Some products require special storage conditions owing to particular physiological characteristics. For example, citrus fruits are stored at temperatures no lower than 4°–5°C. Potatoes are stored at temperatures no lower than 4°C, because at lower temperatures the formation of sugars from starch is intensified, resulting in an undesirable sweetness. Cooled animal products are stored at temperatures close to the freezing point. Meat is stored at temperatures from – 1° to 0°C, and fish from –0.3° to 0°C.

Food products are cooled in chambers or in special units. As the temperature is lowered, the required air humidity is maintained. Fish products are sometimes chilled in ice. Vacuum cooling is sometimes used, particularly for leafy vegetables. Cooled products may be stored for various lengths of time. Fish products keep for two to ten days, and meat (transported in refrigerator cars) may be stored for eight to 12 days. Storage periods for fresh fruits and vegetables vary: seven to 12 days for green vegetables and summer berries; one to six months for summer apples, pears, citrus fruits, and cabbage; and up to one year for potatoes, root crops, and winter apples. When cooled food products are stored, they lose weight as a result of evaporation. This weight loss occurs in fresh fruits and vegetables as a result of respiration.