Frozen Products

Freezing is one of the paramount industrial methods for long-term preservation of food commodities. Because most of the natural foods contain a large quantity of water, the preservation effect of freezing is due not only to the lower temperatures (as compared with chilled foods) but basically to the phase transition of water into ice crystals.


The phase change starts at a temperature of about –1 oC (called Initial Freezing Point) and continues gradually down to very low (cryogenic) temperatures. Freezing rate is of vital importance – slow freezing results in large ice crystals, which cause substantial structural damages of the food tissues after thawing, while fast freezing ensures a fine-grain crystal structure with much less structural damages and minimum drip losses after the product is thawed for further processing and consumption. Тo achieve such a high freezing rate, food engineers invented and developed special Quick Freezing Systems, where products are rapidly frozen down to –18 oC or to lower temperatures, before placing them in refrigerated rooms for long-term frozen storage (which form part of special industrial facilities called Cold Stores or Refrigerated Warehouses). There is not any magic physical meaning in choosing a standard storage temperature of –18 oC (except the fact that it corresponds to 0 oF and that most water in the stored frozen foods is already turned into ice). While freezing prevents the unwanted microbiological processes by killing or suppressing the spoilage bacteria (except some spore or resistant forms), product-specific biochemical changes might still occur. As compared with the other long-term preservation methods (canning, drying, freeze-drying, etc.), freezing is the gentlest mode in terms of keeping the natural nutrients and biological value of foods. A continuous and ubiquitous temperature control must be ensured throughout the entire chain for refrigerated processing, storage, transport, distribution, retail and household handling of frozen foods, which is usually known as Cold Chain or Frozen Food Supply Chain. Hence, while this topic is 'cold' by its nature, it is constantly moved forward by smart scientists, technologists and engineers with warm hearts.


This article was prepared by Kostadin Fikiin of the Technical University Sofia, Bulgaria.

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