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FROZEN FOODS. In the early twenty-first century, frozen foods are an important component of meals prepared and served in both homes and restaurants. They have expanded the kind and quality of meals served and continue to influence food preparations and consumption in this country. The variety of frozen foods in the market reflects the wide use of frozen foods in households. These include ethnic, vegetarian, fast foods, imported gourmet, dietary, and many others.

Early use of freezing occurred in parts of the world, such as Canada, where temperatures in winter drop below freezing for significant periods of time. When hunters brought game animals home in winter, it was possible to freeze the catch by using the outdoor environment as the freezer. It was also convenient on farms where butchering was done. These meats were frozen and used before temperatures moderated. Experiences like this demonstrated the advantages of freezing. Because the storage time was dependent on the weather, this procedure had limitations.

The advantages of freezing as a method of preservation prompted researchers to develop freezing technology. In 1842, a patent for freezing foods by immersion in a brine of ice and salt was issued to Henry Benjamin in Britain. Fish was first frozen in the United States in 1865, and in 1917, Clarence Birdseye began word on freezing foods for retail trade. The use of different refrigerants was one of the early needs examined. The possibility of freons as refrigerants was well received for industrial and consumer applications and led to their early incorporation into household freezers. These early models offered were large in size and were designed to be used for the game and butchering needs of farm families at that time. But soon after their introduction, it was obvious that they were extensively used to store fruits and vegetables, an attractive application for farm households who were growing their own produce. These early models were great successes, and they launched the freezing preservation of fruits and vegetables in this country.

The possibility of freezing preservation of fruits and vegetables became an important interest in the United States, catching the attention of many city apartment dwellers and suburban families who lived in small houses. Unable to accommodate the large-size freezers that appliance manufactures were selling to farm families, these householders teamed up with their neighbors to develop community freezers, where families could rent freezer space in a large freezer-locker rental operation. Although this solved the problem, it was less than convenient.

Questions were raised about the effect of freezing meats, fruits, and vegetables on the quality of the thawed product, including its nutrient retention. The USDA and land grant universities responded to this concern with research studies to assess the impact of freezing on nutrients in fruits, vegetables, and meat, which are summarized by Karmas and Harris. The results of this work showed the nutritional advantages of frozen foods and gave recommendations for freezing methods aimed at retaining maximum quality and nutritional value.

During World War II, homemakers began to join the U.S. workforce in large numbers and appreciated the timesaving advantages of frozen food. The appliance and food industries noted the acceptance by consumers of both freezing preservation of foods and the small freezer sections in household refrigerators. Early models of refrigerators did not offer separate compressor units for the freezer section. As a result, these appliances provided only limited freezing capacity and ability to freeze. The development of appliances with freezing sections that had separate compressors that allowed the freezing section to successfully hold frozen foods in the frozen condition had a major impact on the consumer's ability to store food. The food industry has also responded to the abilities of the new refrigerator models to hold frozen food by introducing frozen foods such as entrees, vegetable, breads, fruits, desserts, juices, snack foods, and ice cream. The refrigerator and freezer combination appliance fits into small spaces and is especially appreciated by those living in apartments and small homes. In the early twenty-first century, few refrigerators do not include a freezer on a separate compressor.

In microwave heating, foods are placed in an electromagnetic field when they are positioned in the oven cavity and the microwave energy is turned on. Heat is generated by molecular friction among the free water molecules in the food load. Since a frozen food has a very small amount of unfrozen water that attracts the microwave energy first, the heat is generated in a small part of the food load and is rapidly absorbed by the frozen part. In frozen foods, a large part of the water is in the form of ice. While water readily absorbs microwaves, ice does not. Some of the water in frozen foods does not freeze; this may be due to the salt content. The unfrozen water absorbs microwaves quickly in the microwave appliance. As a consequence, the use of microwaves to thaw and cook food may result in "runaway heating," a situation in which the unfrozen water containing salts is boiling while next to it, areas of ice exist. To prevent this, a defrost program is recommended; this feature exposes the food load to microwave energy for a short time, then turns microwaves off for a slightly longer time, allowing the heat to be conducted to the ice. This cycle is repeated until thawing is completed and does not usually produce runaway heating.

See also Birdseye, Clarence; Microwave; Preparation of Food; Preserving.

Gertrude Ambruster