Temperature conditions of freezing foods. Part II

2011-12-06

Rapid cooling of wines and beverages is carried out by placing them briefly in LTC (low temperature chamber). Time of the readiness of wine for consumption is determined by its variety and temperature in the LTC. Let’s also consider freezers and departments or sections providing conditions for rapid freezing of food - four stars *(***). Freezing is rapid in such LTCs if the product completely freezes up to -18 ° C at its whole depth within 24 hours. Rapid freezing at naturally cooling occurs at temperatures of -24 ° C and below. Typically, in the mode of freezing the refrigerator-freezer operates continuously and the temperature in the freezer can fall to -38 ° C. In cases of forced cooling with accelerating technologies the rapid freezing can occur at temperatures below -20 ° C. The above examples confirm that the fourth big star now does not mean -6 ° C. It only confirms the possibility of rapid freezing. Technology of freezing and storage of foods having plant and animal origin significantly affects their taste and nutritional quality when consumed after thawing. Any faulty freezing and storing frozen food can cause an alimentary toxicosis of varying degrees of severity, if foods with defects or being infected by bacteria were kept on the fridge for storage. Cold only slows down the bacteria development, but does not kill them. It is known that some pathogens are reproduced well at temperatures -6 ° C and even below. When frozen the product it freezes faster outside, but slowly inside. Before freezing foods it is recommended to split them into thin pieces or slices whose thickness does not exceed 4 cm for a single use and deep complete freezing. Having such a thickness, slices of products freeze at the full depth – up to -18 ° C for 24 hours. Most experts believe that the vital activity of bacteria is suspended at -18 ° C. Experts guess that temperatures of - 24 ° C for rapid freezing and -18 ° C for long term storage are enough in living conditions. Further temperature lowering of freezing and storage is impractical, as winning in the extension of storage will not be significant but the increase of the power consumption will be meaningful. Each degree of any temperature depression requires the additional power consumption. In addition, the increased dilution in the cooling system and increasing probability of the tightness violation deal with the drop of the refrigerant evaporation temperature. Thereafter, taken in the whole, the refrigerator-freezer allows short time storage of everyday products at positive temperatures. It also allows keeping fresh meat, fresh fish, vegetables and fruits in a "dry" and "wet freshness" for a long time, to keep frozen for some months and almost unlimited variety of wines in the mode of the "cellar" with the recommended temperature of 8 ° C to 12 ° C and relative humidity from 50 to 80%. Freezing of products begins when the temperature in the chamber or compartment is below 0 ° C. This is the ultimate freezing point of pure water and melting ice. A thin crust of ice is formed on the surface of the product at low temperatures close to 0 ° C, but freezing does not occur in the depth. The range of low temperatures around 0 ° C is called the zone of a "dry freshness" and above-zero temperatures – the zone of the "wet freshness." Conditions of the "dry freshness" and "wet freshness" are used for the best and most durable retaining of the original qualities of fresh products in different models of the household refrigeration equipment made by various companies. Frozen fish in a "dry freshness" is stored in a fresh state for a week. Freezing fish can be carried out in low compartments or low temperature chambers with any labels. Some fruit and vegetables in a "wet freshness" conditions can be stored for months.