First of all, there is the sea and coastal freezing. Sea fishing is carried out directly on the fishing vessel if it is away from the coast for a long time. For this, powerful freezers are installed on the ship.
Coastal freezing is carried out in the factory after delivering raw materials to the shore. During transportation, the fish is in cold seawater.
Natural and artificial can distinguish the factory methods of freezing seafood.
In natural conditions, on a selected open area (often near the fishing site), snow is poured with water to form a smooth ice surface. Then the fish is laid out in one layer and remains there for several hours until it freezes completely. The required air temperature for this method is -15 degrees. At present, this method is used extremely rarely and only in those areas where regular frosts persist.
With artificial freezing, it is carried out in extraordinary chambers at a temperature of no more than -23 degrees. The fish is also placed in one layer on galvanized iron shelves. In some, freezing structures can hang fish on hooks or special carts. The freezing process is relatively slow, up to several days, and sudden temperature changes are undesirable.
To increase the efficiency of artificial freezing, unique installations are used. So, there is an intensive air freezing: salmon is placed on metal baking sheets with lids, which are placed between two surfaces where the refrigerant circulates. In some cases, the refrigerant is circulated over vertical or horizontal tiles in compact tile chambers.
During brine freezing, special solutions of table salt are used, the concentration of which varies between 18-22%, and the temperature is from -16 to -20 degrees. Salmon is dipped into such solutions and placed in the freezer. This is a relatively fast method of freezing, but at the same time, the fish is salted, which is not always in demand by the end consumer.
The principle of using boiling refrigerants for freezing is based on the atomization of liquid nitrogen in unique installations. The method is also relatively fast but very expensive and rarely used.
The most common method in modern processing plants is shock. The essence of shock freezing is not so much to use lower temperatures but to significantly increase the cooling rate. Salmon is frozen according to this principle: it is gradually cooled when the temperature drops from +20 to 0 degrees - this is the initial stage of freezing. Then within 20 minutes, the temperature drops another 5 degrees; this happens within 1.5 hours. Further, the temperature drops to about -18 degrees. And then the final stage is shock freezing when the temperature reaches -30 degrees.
With this method, salmon fractions do not crystallize so intensively, which positively affects their quality.
Today, most fish and seafood producers use the shock freezing method. If we talk about salmon, then this method is used by the leader of the fish processing industry, the company "East Coast" (Bering Seafood), which catches wild Pacific salmon. Thanks to shock freezing, the appearance, freshness, naturalness, valuable properties, and taste of redfish are preserved. It is not for nothing that the MSC standards confirm the quality of salmon and red caviar of the Vostochny Bereg brand - the Marine Stewardship Council and international certificates.
Another method of freezing is glazing, in which a thin ice shell is formed in the fish, protecting it from external negative factors and the oxidation of the fatty layer.
An alternative option is an irrigation with the same water while maintaining the conditions in the room no more than -12 degrees. After processing, the fish is placed in chambers to freeze the liquid.
Not all freezing methods are used; the natural one has practically lost its power. Nevertheless, all of them have the right to exist, and all ensure the safety of salmon and its quality.