According to the German Institute of Frozen Products, the turnover of frozen foods (excluding ice cream) in the food, food and peripheral markets has increased by almost 60% in the past decade and reached 3.136 million in 2007. Ton. Per capita consumption rose from 26.6 kg to 38.1 kg, surpassing the 38 kg mark for the first time. The main advantage of frozen products is that consumers can store frozen foods for a long time without food quality changes or nutrient loss. More importantly, frozen products can be stored until they are needed.
Many foods can be stored frozen and preserved, regardless of season or time. In addition to years of freezing fish, vegetables and potatoes, today's frozen convenience foods include snacks, baked goods and pizza.
Freezing is mainly to help preserve food. Freezing is also an important process in some cases, such as freezing dried coffee. The key factor in determining the quality of frozen products is not only whether the raw materials are suitable for freezing, but also the selection of suitable freezing techniques. Frozen foods rely not only on the right temperature, but also on timing. The main difference in current refrigeration technology is the rate of heat transfer. The focus of frozen foods is to reduce the food to a 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 foods will change. Not only will vitamins and nutrients be destroyed, but the 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 slightly damage the food matrix. In order to do this, the freezing rate, that is, the ice interface, moves at least one centimeter per hour in the food. In general, standard home freezing equipment freezes at an average rate of 0.1 cm per hour.
Cautiously save
Industrial frozen foods can be used in the following ways: airflow freezing, contact freezing, and cryogenic freezing. Airflow freezing and contact freezing are conventional methods, and the freezing low temperature is mainly realized by a refrigeration compressor. This method uses a channel type freezer or a fluidized bed to freeze through a gas stream. The food to be frozen is placed on a conveyor belt, and cold air is transferred from the passage and flows through the food. Channelized airflow is suitable for all packaged, unpackaged, regular shaped and irregular shaped foods. When the fluidized bed is frozen, the bottom trough pushes the cold air upwards, and the loose, unpackaged food moves back and forth and is frozen by the cold air. The use of a refrigerated belt, a flexible steel belt or a rotating cylinder is another conventional freezing method in contact freezing. In this method, the packaged food is placed between the metal plates, the coolant flows between the metal plates, and the metal plate is cooled to about minus 40 °C. Contact freezing is mainly used for freezing blocky foods such as fish fillets or creamy spinach.
Low temperature freezing, endless potential
More and more frozen products are being sold in small pieces. Pasta, rice, seafood, vegetables or a mixture of these foods are all dispersed and frozen, which can be achieved by cryogenic freezing. The food to be frozen is placed in liquid nitrogen (minus 196oC) or liquid carbon dioxide (minus 78°C) and frozen into high quality monomeric frozen food. The inherent principle of cryogenic freezing is relatively simple: at the moment of entering the freezer, the liquid nitrogen boils and the carbon dioxide sublimes, and the energy (heat) required for the process is taken from the food, causing the food to be cooled and eventually frozen.
The cryostat is different from the traditional freezer because the freezing rate of the cryostat is extremely high and can reach 5 cm per hour. For example, the starter for making cheese and yoghurt can be quickly frozen into loose granules. As temperatures drop rapidly, up to 95% of microorganisms can survive. In this way, the frozen starter is easy to store, transport and use during the fermentation process. The freezing capacity of the traditional freezer is fixed at the time of design. The freezer has a wide range of freezing and can freeze many new products. For example, pectin of ice cream can be produced by using liquid nitrogen to freeze. The surface of the ice cream is first frozen at a low temperature. If the ice cream is placed in the pectin at this time, the pectin will spread evenly on the surface of the ice cream. This freezing method can thicken the pectin coating of the ice cream.
This modern refrigeration technology has unlimited potential, but we must remember that temperature assurance is equal to quality assurance. The chain of refrigeration links food producers, retailers and consumers closely. We must keep in mind that the quality of the product can only be guaranteed through proper storage and transportation.