Refrigerated Foods Food Freezing And Processing

In high latitudes it is possible to freeze foods simply by leaving the product outside in winter. This familiarity with food freezing resulted in a general feeling that such a simple process needs little planning or care in product selection, processing, packaging, or subsequent storage and can be accomplished with the minimum of skill. The enormous amount of scientific research put into these three P's (intrinsic Product quality, Processing, and Packaging) by food scientists has resulted in frozen raw materials and products, now increasingly available across the world, meeting the needs of the most sophisticated consumers. Equally important are the three T's (Time, Temperature, and Tolerance), which govern the practical shelf life (PSL) of all frozen products.

The advent of mechanical refrigeration (1) led by the Linde air compressor in the 1850s (capable of maintaining temperatures of about - 9°C—the temperature at which mold activity can be ignored over short periods) made it possible to emulate winter conditions in high latitudes across the temperate and tropical regions irrespective of season. A frozen food industry developed, with its capability of transporting products such as beef, lamb, fish, shellfish, and butter around the world and particularly across the Tropics.

The pioneer of the retail frozen food industry, an American named Clarence Birdseye, invented a multiplate froster that enabled commercial quantities of food to be frozen rapidly and brought down to - 18°C, which he specified as the warmest temperature at which this new "frosted" food should be stored (2). Today, some 70 years after the launch of the first commercially frozen retail frozen products in Springfield, Massachusetts (3), there has been only little change in the basic precepts of this now large industry. The results of a massive research program, carried out at the U.S. Department of Agriculture (USD A) Western Research Laboratory in Albany, California, in the 1950s, known as the Time-Temperature Tolerance (T-TT) program, validated Birdseye's original prescription of — 18°C as the accepted temperature for the industry and has been immensely influential in defining custom and practice throughout the industry (4). Later researchers (5) favored colder temperatures for long-term storage of fish, especially fatty fish such as salmon. Many cold stores have been built capable of holding temperatures of - 30°C and, in the case of surimi (to preserve the white color) for the Japanese market, temperatures as cold as — 60°C.

The first textbook on food freezing (2) omitted two products that, when developed later, now play a large role in the industry—French fries and frozen concentrated orange juice. Sources of information on food freezing technology include the International Institute of Refrigeration (IIR), the proceedings of which cover the whole gamut of refrigerants; refrigerating equipment; cold store construction; road, rail, and sea transport of frozen foods; and the characteristics of various products during freezing, storage, and thawing (6). In the United States the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) handbooks (7) summarize published re search and provide essential background information on refrigerant characteristics. The IIR has also published a concise guide to the processing and handling of frozen foods (8).

Following the successful T-TT program in the 1950s, attention was drawn to the importance of other factors apart from time and temperature—the three P's (5). Subsequent publications (9,10) have elaborated on these developments and advanced our knowledge of the science and practice of food freezing, storage and transport.

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