The Technical Principles Of Frozen Foods

Refrigerated foods primarily utilize low temperatures to inhibit the growth and reproduction of microorganisms, thereby extending the food's shelf life. In a low-temperature environment, the metabolic activity of microorganisms slows down, reducing the rate at which food spoils. Furthermore, low temperatures can slow the rate of chemical reactions within the food-such as lipid oxidation and protein denaturation-thereby preserving its nutritional value and texture. The temperature range for refrigerated foods typically falls between 0°C and 10°C.

Frozen foods, conversely, utilize even lower temperatures to freeze the water content within the food, thereby achieving long-term preservation. During the freezing process, the water in the food forms ice crystals; these crystals inhibit the growth and reproduction of microorganisms, allowing the food to retain its freshness for an extended period. Frozen foods typically require storage temperatures below -18°C.

Freezing methods include rapid freezing (quick freezing) and slow freezing. Rapid freezing produces smaller ice crystals, which cause less damage to cellular structures; consequently, the quality of rapidly frozen foods is consistently superior to that of slowly frozen foods. Rapid freezing typically requires lowering the core temperature of the food to approximately -5°C within 30 minutes, followed by storage in an environment maintained at -18°C. Due to the rapid rate of temperature reduction, the water within the food enters a "supercooled" state; the ice crystals formed at this stage are minute-small enough not to cause significant damage to the food's cells. The core principle behind this process is to ensure the food passes quickly through the "maximum ice crystal formation zone" (i.e., the temperature range between -1°C and -5°C).

Generally, -12°C is considered a safe temperature for the frozen storage of food, while temperatures below -18°C are even more effective at preserving food quality. Currently, the majority of frozen food storage facilities-both domestically and internationally-maintain temperatures below -18°C, with a common operating range spanning from -18°C to -35°C.

TTT stands for Time-Temperature-Tolerance; this concept is used to assess the tolerance of food quality to varying temperatures across the different stages of the cold chain. The thawing process is another critical factor influencing the quality of frozen foods. During thawing, one should strictly avoid repeated cycles of freezing and thawing, as this can cause ice crystals within the food to enlarge, thereby damaging the food's cellular structure and compromising both its texture and nutritional value.