Fundamentals of Low-Temperature Food Preservation

Abstract

Publisher Summary This chapter cites a great many occurrences associated with the freezing, storage, and thawing of foods. To understand how the freezing process brings about changes in food systems, thorough knowledge is needed of the characteristics and interrelationships of food constituents. The chapter presents the general classification and characteristics of food systems that will provide a logical basis for evaluating detailed changes in specific food systems. Food systems are divided into two major groups: gross intact tissue systems and small-particle systems. Small particle systems are further subdivided into dispersions and undispersed solids. The chapter briefly illustrates some changes in selected food systems resulting from the freezing process. An attempt has been made to draw some general conclusions concerning the possible means by which food deteriorates during the entire freezing process (freezing, frozen storage, thawing) and each phase of the freezing process is considered separately. The removal of heat energy from foods being frozen has two basic effects: a decrease in temperature and a change of state from water to ice. During the freezing of any complex material, these two consequences of heat removal are inseparable. However, it is of theoretical interest to determine how the consequences of a decrease in temperature with a change of state of water to ice compare with the consequences of the same decrease in temperature with no change of state. This approach enables the causes of freezing damage to be determined more accurately. The chapter briefly reviews the technological aspects of the frozen food industry. The three most common types of freezing systems are air blast (gaseous coolant), indirect contact (solid coolant), and direct immersion (liquid coolant). Each type possesses certain advantages and disadvantages.