Chapter 14 - Food Refrigeration and Freezing

Abstract

Cooling and freezing cannot improve a fresh vegetable, fruit or meat product, and the best that can be achieved is to keep it near to the condition in which it entered the cooling process. Storage in the frozen state enables products to be kept for longer than maintaining chilled conditions. Freezing reduces bacterial degradation reactions to a very low level but causes structural change in the product due to the formation of ice crystals. The cells of animal and vegetable products contain a water solution of salts and sugars. The texture and moisture content of the product after thawing will differ from that of the fresh product, and for some products it also results in weight loss in the form of “drip loss.” Different freezing methods are used to minimize these effects. Products in regular-shaped packages, such as ice-cream in flat cartons, are pressed between horizontal, flat, refrigerated plates. These can be opened apart slightly to admit the product and are then closed by hydraulic rams to give close thermal contact. When freezing is complete, the plates open again to remove the packs. The vertical plate freezer is used for a loose product such as wet fish, which is packed into the gaps between the plates.