Food Freezing

Freezing has long been established as an effective method for the long-term preservation of foods. It has the potential to maintain quality and nutritional characteristics close to those of fresh foods. Although refrigerated storage has been developed to a stage where high quality can be maintained for a few weeks, when extended shelf life is required of a preservation technology, the most commonly used methods are freezing, thermal processing, and canning. It is generally accepted that of these three methods, freezing is superior (1). Properly conducted freezing retains much of the flavor, color, texture, and nutritive value of food. The activity of microorganisms is much reduced, and, while frozen, many enzymes also have reduced activity. However, the freezing process can disrupt the control systems that influence enzyme action, leading to undesirable changes during thawing. Where this is a problem, special techniques may be used to destroy or reduce enzymic activity before freezing. The consequences of thawing are mentioned because, with the exception of frozen commodities that are consumed directly (such as ice cream), normal freezing preservation requires that products be thawed before they are used.

Long before commercial application, refrigeration was used as a preservation technique. An early report is found in the She King, Chinese poetry written in 1100 B.C. (2). The earliest refrigeration agent was natural ice from frozen rivers and lakes and mountain snows. Natural refrigeration was used to preserve meat, game, fish, and, more recently, eggs, vegetables, and fruits. It has long been accepted that low temperatures reduce the rate of spoilage of food products compared to higher temperatures, and those who reside in colder climates have tended to expect food to store for longer times than those from hot climates. Modern progress in the refrigerated storage of foods, however, required the development of systems capable of producing low temperatures on demand.

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