| Fish Processing Industry |
 When fish temperature decreases to -8 - 10°C and lower, such fish is called frozen fish. Most of water in fish tissues turns into ice in the course of the given process. This procedure is applied in order to preserve fish for a longer time. Freezing is applied to live or fresh fish and the temperature of frozen fish falls down to -18 - 20°C and lower. The quality of frozen fish depends on the quality of raw materials, the ways of refrigeration, the rate of refrigeration and storage conditions. Fish frozen during a refrigeration process is characteristic of crystallization of water substratum and its drying off. Crystallization is initiated when the temperature is lowered below the freezing point of tissue juice. During a refrigeration process, the volume of water in tissues increases as many as 9-10 % and solidification of the product takes place, depending on the amount of the water frozen in which, in its turn, depends on temperature. Most of water exudes from fish freely or as a juice constituent. In this way about 25 percent of tissue juice off the total mass of fish is lost. Alongside, nutritional and taste properties are lost, furthermore the consistence of such a fish becomes dry and tough.  Freezing rate is a very important factor in choosing refrigeration equipment as the reduction of freezing rate results in the change of the size and distribution of ice crystals. The size of crystals and lesions in tissue composition are directly interdependent. The utmost structural lesions result from slow freezing. In this case, large ice crystals determining disarrangement of peripheral layers are formed. The most prevailing methods of fast refrigeration of fish are contact freezing and freezing by air. The latter occurs when air is intensely blown at a product in a freezing tunnel at the temperature no lower than -35°C. In the case of contact refrigeration, a product is frozen by means of coming into contact with a cold surface. Vertical and horizontal plate freezers are used to this end. The truth is that the given method is unsuitable for certain kinds of fish when pressure between the plates causes a mechanical violation of fish itself. This method is proper for freezing fish fillets, also for block freezing. Air refrigeration usually involves tunnels (IQF) wherein freezing takes place by means of intense air flows and due to a great difference in temperatures. Refrigeration tunnels can be spiral, of the corridor type. Spiral tunnels are distinguished for their compact size. One of the world’s leading producers of tunnels is Frigoscandia.  When designing refrigeration systems for fish factories and processing plants, our specialists evaluate all the aforementioned factors apt to influence refrigeration processes and suggest an optimum variant for retaining valuable nutritional properties of fish or fish products as well as select the most cost-effective refrigeration system for the customer. Refrigeration equipment is designed in compliance with EU ecological and sanitary norms, technical regulations and design directives and rules. |