Controlling the temperature of refrigeration can ensure the quality of food. The cold chain closely links food producers, retailers and consumers. The development potential of modern refrigeration technology is infinite, and the quality of products can only be guaranteed through reasonable storage and transportation.
Customers in frozen and refrigerated food processing industry, food trade industry, catering industry and consumption field have high requirements for the quality of frozen and refrigerated food, and the field of frozen and refrigerated products needs a comprehensive technology with different temperature requirements.
Frozen and Frozen Food Industry According to the statistics of the German Institute of Frozen and Frozen Products, the turnover of frozen and frozen food (excluding ice cream) in food trade and surrounding catering markets has increased by almost 60% in the past decade. In 2007, it reached 3136,000 tons, and the per capita consumption rose from 26.6 kg to 38 1 kg, exceeding the scale of 38 kg for the first time. The main advantage of frozen and refrigerated products is that manufacturers and distributors can store frozen and refrigerated foods for a long time without quality change or loss of nutrition. More important frozen and refrigerated products can be stored until they are needed.
Frozen food is not affected by season and time. Many foods, such as fish, meat and vegetables, have been frozen and stored for years. Now there are snacks, baked goods, freeze-dried coffee and pizza.
The key factors that determine the quality of frozen and refrigerated products are not only related to whether the raw materials are suitable for frozen and refrigerated, but also helpful to the preservation of food. In some cases, freezing and cold storage are also an important processing process.
It is also important to choose the appropriate freezing and cold storage technology. Frozen food depends not only on whether the temperature is appropriate, but also on the timing. At present, the main difference of freezing and refrigerating technology lies in thermal conductivity, and the key point of freezing and refrigerating food is to reduce the food to the core temperature of at least MINUS 18 degrees. If the freezing process is too long, large ice crystals formed by water molecules will destroy cell membranes and tissues, and the structure and shape of frozen food will change, not only vitamins and nutrients will be destroyed, but also food will lose its original taste. However, if the freezing process is particularly fast, the water will freeze into very small crystals, which will only cause slight damage to the food substrate. In order to do this, the freezing and refrigerating speed, that is, the moving speed of the ice interface in food should reach at least one centimeter per hour. Generally speaking, the average freezing speed of standard household refrigeration equipment is 0.65438 0 cm per hour.
The low temperature of refrigeration is mainly realized by refrigeration compressor. In this way, the channel freezer or fluidized bed is mainly used for freezing and cold storage by airflow. Put the food to be frozen on the conveyor belt and keep it carefully: the following methods can be used to freeze food in industry: airflow freezing, contact freezing and low temperature freezing. Airflow refrigeration and contact refrigeration belong to radical ways. Cold air is sent out from the passage and flows through the food. Channel airflow refrigeration is suitable for all packaged foods, unpacked foods, regular foods and irregular foods. When the fluidized bed is frozen and refrigerated, the bottom net groove pushes the cold air upward, and the loose unpacked food moves back and forth and is frozen by the cold air. Using refrigeration belt, flexible steel belt or rotary cylinder is another traditional refrigeration method in contact refrigeration. In this method, the packaged food is placed between the metal plates, and the coolant flows between the metal plates to cool the metal plates to about MINUS 40℃. Contact refrigeration is mainly used for the refrigeration of bulk foods such as fish fillets or creamy spinach.
This can be achieved by freezing at low temperature. The food to be frozen and refrigerated is frozen and refrigerated in liquid nitrogen (minus 196℃) or liquid carbon dioxide (minus 78℃) to form high-quality monomer quick-frozen food. The internal principle of cryogenic refrigeration is relatively simple: at the moment of entering the freezer, the potential of cryogenic refrigeration is endless: more and more frozen products are sold in small pieces. Spaghetti, rice, seafood, vegetables or a mixture of these foods are distributed in cold storage. Liquid nitrogen boils and carbon dioxide sublimes. The energy (heat) needed in this process is obtained from food, which leads to the food being cooled and finally frozen. Low temperature freezer is different from traditional freezer because of its extremely high freezing rate. It can reach 5 cm per hour. For example, starter cultures for cheese and yogurt can be quickly frozen and refrigerated into loose particles. Because the temperature drops rapidly, up to 95% of microorganisms can survive. In this way, the frozen starter is easy to store, transport and use in the fermentation process. The freezing and refrigerating capacity of radial refrigerator are fixed in design. The low-temperature freezer has a wide range of freezing and refrigerating, and can freeze and refrigerate many new products. For example, liquid nitrogen can be used to make pectin for ice cream. First, the surface of ice cream is frozen and refrigerated at low temperature. If pectin is added to the ice cream at this time, the pectin will be evenly dispersed on the surface of the ice cream. Freezing and refrigerating technology can thicken pectin coating of ice cream and improve product quality.
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