Since ancient times, people have been looking for ways to store different foods without losing their nutritional value. In different countries, under different climatic conditions and nutritional characteristics, methods long-term storage, the most effective of which was considered freezing. In ancient Russia, for this purpose, they learned how to use blocks of ice that were cut down in winter on rivers or artificially flooded slides and formed into deep cellars. This ice did not melt even in the summer, serving as a kind of predecessor of the modern refrigerator.
Currently, the preservation of products through various methods of freezing widely used throughout the world . And not only for the purpose of their long-term storage, but also for changing their condition in preparation for processing, for separating excess liquid, and also when creating products, for preserving the taste and quality of which frost is necessary - ice cream, for example.
The essence of the process of freezing lies in lowering the temperature below the cryoscopic one, the one at which the water contained in the frozen products crystallizes, turning into ice. Of course, because of the difference in the composition and consistency of different foods, there are a number of different methods and approaches to the process of freezing. The most popular and used methods are recognized, in which low-cost and high-quality freezing of products is carried out - complex methods.
In the modern world, special technologies have been developed that allow the maximum preservation of useful substances and vitamins contained in products subject to freezing. Accordingly, the very process of freezing a particular product takes a certain amount of time, because meat, fish, seafood, berries, vegetables, mushrooms, semi-products react differently to a decrease in temperature. In addition, the duration of the freezing procedure is affected by the thickness of the package. The product is correctly frozen when in its center the temperature drops to -6 degrees Celsius.
To freeze products today, two main methods are used : air freezing and the use of refrigerants. The first method is the 70-year-old method of shock freezing. Its main advantage is that there is no need for preservatives, and due to the high freezing speed the consistency and taste of frozen products almost does not differ from fresh ones. The technology of shock freezing is also successfully used in the preparation of ready-made dishes, which, before serving, need only be heated in a microwave oven.
Complex methods of freezing are also used for quick freezing of products with a gentle consistency, in application to which a press is not allowed - seafood, semi-finished products from sliced ​​vegetables, fish fillets, berries and fruits. With this method of freezing, quality products are obtained in fluidization freezers. Liquid and pasty products - pastes, pastas, ice cream - are frozen in other special devices called friezers.
A method using coolants includes cryogenic freezing, during which the products, upon direct contact, cool safe inert substances. It also requires a comprehensive approach, to reduce costs, a combined cooling method is used: first with the help of cryogenic substances, and then with cold air. An example of such equipment can serve as a refrigerator with a frost based on liquid nitrogen.
Rapid scientific progress every year adds to the already practiced methods of freezing something new, improving the process itself and the methods of conducting it to maximize the value and nutritional value of frozen foods. And one day, of course, will be found the optimal integrated method, the application of which will finally erase the line between fresh products and those subjected to frost.