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Cooling and freezing

The essence of this method of conservation is that at low temperatures the vital activity of microorganisms is suppressed, the activity of enzymes decreases, and the course of biochemical reactions slows down.

At low temperatures, characteristic of cooling, in fruits and vegetables, the respiration processes continue, albeit slowly, that allow them to remain fresh for several weeks and even months.

Cooling carried out using artificial or natural cold. When stored in glaciers or chambers with artificial cold, the product temperature drops to 0 ° C (with fluctuations of ± 2-3 ° C). At this temperature, the cell sap does not freeze.

Freezing Is a canning method that uses low temperatures to ensure complete or partial transformation of cell sap into ice. The faster the freezing process is carried out and the lower the temperatures are reached, the better the quality of the frozen product.
When freezing, an almost complete cessation of the activity of microorganisms occurs, many of them die, Of course, the complete death of all microorganisms does not occur. Some of them remain intact, while some are able to form spores and maintain their vitality.

When the cell sap freezes, ice crystals form inside and outside the cells, which lead to mechanical damage to the membrane. When the temperature rises, whole microorganisms develop again and this can lead to product spoilage. When storing frozen products, it is necessary to strictly control the storage temperature, ensure good sanitary conditions in the preparation rooms and chambers, and use only high-quality raw materials for freezing.

The suppression of the vital activity of microorganisms lies in the fact that in frozen food products most of the moisture is converted into a solid state and microorganisms that feed on the osmotic route are deprived of the opportunity to use the hardened food products.
Due to the absence of a liquid phase, the activity of enzymes ceases, as a result of which biochemical processes are suspended.

It has been found that after the cryoscopic temperature for a given product is reached, a subsequent halving of the temperature leads to freezing of about half of the remaining moisture.
For example, if the cryoscopic temperature of the product is –2 ° C, then when the temperature drops to –4 ° C, 50% of the moisture will freeze.
With a further decrease to -8 ° C, 75% of the initial amount of moisture will turn into ice.
Calculations show that 87.5% of moisture will freeze at a temperature of -16 ° C, and 93.8% at a temperature of -32 ° C.
Already at -16 ° C, most of the moisture will turn into ice, therefore, from a practical point of view, there is no need to bring the temperature to -32 ° C.

The generally accepted temperature level, to which almost all frozen foods are brought, is - 18 ° С, since for some food products the cryoscopic temperature is - 2 ° С.

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