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The basic Knowledge of food refrigeration
The commercial refrigerator is a tool that provides food preservation. Different foods require different preservation temperatures. Therefore, the refrigerator temperature should be set according to the type of food stored. For example, green leafy vegetables 12 degrees, tropical fruits 10 degrees, cooked food 8 degrees, beer drinks 4 degrees, fresh meat -18, fish and shrimps 0 degrees, etc. In principle, that has nothing to do with the season. Freezer temperature range is -4 to -24 degrees (three star -18 degrees, four star -24 degrees), and the refrigerator temperature range is 5 to 15 degrees.
Commercial refrigerator is divided into display cabinet and refrigeratd freezer
Display cabinets are divided into:
1. Vertical display friidge, suitable for the display and storage of beverages and beer in the supermarket;
2. Horizontal display freezer, suitable for storage of ice cream and dishes.
Refrigerators and freezers are divided into:
1. Dual temperature conversion cabinets, which can only be adjusted to refrigerated or frozen;
2. Dual temperature dual cabinets, taking into account both refrigeration and freezing.
The storage object of the freezer is food. From common sense, we can know that different foods have their proper storage temperature and humidity. Therefore, to do a good job of food refrigeration, we must first understand the composition and characteristics of food. The ingredients of food can be divided into organic and inorganic, including organic, protein, sugar, fat, vitamins, etc., and inorganic, including water and minerals. During storage and transportation, the sugar in fruits and vegetables is oxidized by the oxygen in the air to carbon dioxide and water due to respiration and releases heat: when hypoxic respiration, alcohol and carbon dioxide are generated.
Fat oxidative decomposition process is related to temperature. When the temperature is high, the oxidation proceeds faster. Therefore, lowering the temperature can guarantee the quality of fat. Moisture in food exists in two forms, free water and colloidal water. Free water is contained in food juices and cell fluids and is a good solvent. Colloidal bound water is water located in the colloidal space and the water film around the colloidal particles. Colloid-bound water has different properties from free water. It loses the fluidity of ordinary water and has a smaller specific heat capacity than free water. Its freezing point is much lower than that of free water', generally below -25℃. The food contains a lot of water, which forms good conditions for the growth and reproduction of microorganisms, which can easily cause food quality changes.
The principle of food preservation in the freezer
1. Fresh food is stored at room temperature. Due to the action of microorganisms and enzymes in the food, as well as respiration and chemical action, the beneficial ingredients of the food will be consumed and spoilage will occur. The life activities of microorganisms and the catalytic action of enzymes need to be carried out under certain temperature and moisture conditions. If the storage temperature is lowered, the growth and reproduction of microorganisms will be slowed down, and the enzyme activity will be weakened, which can extend the storage period of food.
2. In addition, the metabolic process of microorganisms will be destroyed at low temperatures, and toxic substances and other peroxides accumulated in their cells can cause the death of microorganisms. When the temperature of the food drops below -18°C, more than 90% of the water in the food will become ice, and the ice crystals formed can also destroy the microbial cells in a mechanical way, causing them to lose nourishment or part of the protoplasm solidification, dehydration, etc , Causing microbial death. Therefore, freezing food in the freezer can maintain the original quality of the food for a longer period of time.
3. The refrigeration process of food refers to the cooling, freezing, cold storage and thawing of food, that is, the method of using low temperature to store and process food. Cooling is to quickly reduce the temperature of the food to the specified temperature, but it should be higher than the freezing point of the food juice. Generally, the temperature of the cooled food is 4 to 0°C. At such a temperature, not only can the shelf life of the food be extended, but also the freshness of the food can be kept to the maximum.
4. However, at this temperature, some microorganisms can still grow and reproduce, so the cooled fish and meat food can only be kept for a short time. Freezing is to freeze most of the water contained in the food into ice, which is to quickly reduce the temperature of the food to the freezing point of the food juice and reach a certain fixed temperature. After the food is frozen, due to the low temperature of the freezer and lack of water, some microorganisms are killed, and the rest of the microorganisms are extremely weak. Therefore, the frozen food can be preserved for a longer period of time. Freezing is divided into quick freezing, quick freezing and general freezing according to its speed. Among them, quick freezing and quick freezing can ensure the quality of food and make the food more reversible. Refrigeration is to store foods for different periods of time while maintaining the final temperature of food cold processing.
5. According to the final temperature of cold processing, the refrigeration of food in the freezer can be divided into two types: cold storage (high temperature refrigeration) and frozen storage (low temperature refrigeration). Thawing is to melt the ice crystals in the frozen food into water and restore it to the fresh state before freezing. Defrosting is also the reverse process of freezing. For frozen products used as raw materials for processing, it is generally only necessary to increase the temperature to half-thaw.
Contact Person: Mr. Joe Leung