Introduction
The idea of exploiting the protective action of low temperatures to extend the storage time of food was already bobbing in the minds of our ancient predecessors.
Freezing of food
Cold, like heat, is a hostile condition to microbial life. While the high temperatures lead to the almost total destruction of these microorganisms, the cold can only slow down their proliferation. When the cooling action fails, the microbes in fact begin to develop again, accelerating the decomposition processes of the food. Cold also associates discrete bactericidal properties with this bacteriostatic activity, especially when low temperatures are maintained for a long time.
Obviously, the effectiveness of freezing is greater the lower the temperatures reached by the food. The lower the temperature, the higher the percentage of frozen water. By depriving the bacteria of this essential element for life, it is therefore possible to preserve it for a long time. Foods.
Freezing begins at temperatures between -0.5 and -2.8 ° C and, as these drop, an increasing number of water molecules are affected. However, a certain quantity, which varies from food to food, remains liquid even at temperatures of maximum freezing, due to its bond with the constituents of matter. The permanence of minimal quantities of water therefore allows a slow progress of the deterioration processes.
Quick freezing
Freezing can take place more or less quickly, causing various consequences on the chemical-physical integrity of the food.
- When the freezing process is too slow, the water forms ice macrocrystals which can damage the structure of the food, with consequent loss of nutritional principles and organoleptic characteristics. Due to this phenomenon, once defrosted, foods appear watery and unappetizing.
- In rapid freezing, small crystals are formed, which do not significantly alter the appearance, palatability and chemical-biological constitution of the food.
The slow freezing method was soon abandoned and today even home freezers are equipped with a button for rapid freezing, which allows a sudden drop in temperature, keeping it around -30 ° C for as long as necessary to freeze the food. .
Frozen or frozen
Deep freezing is a preservation technique based on rapid freezing. A food can be said to be frozen when it has precise quality requirements:
- it must have been frozen with an ultra-fast technique
- it must be ready for consumption
- it must be kept constantly at a temperature not exceeding -18 ° C
- it must be kept in a hermetically sealed package, from origin to sale
Freeze the food
Domestic freezers are generally set at a temperature of -18 ° C which, as we have seen, is sufficient to optimally preserve the industrially frozen product. However, these values are not sufficient for a good freezing of fresh food.
Optimal freezing in the home must therefore rely on the rapid freezing method, integrated in most freezers. The key that activates this function must be kept active for the six hours preceding the introduction of the food to be frozen, carefully placed in safe packaging. In any case, it is advisable to carefully read the instructions in the instruction manual, as the characteristics of the freezers vary from model to model.
General classification of the various compartments:
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CONTINUE: Shelf life of frozen foods "
Freezing food "
