Freezing means changing the liquid content found in most of the fish’s body to ice. Fish will begin to freeze at temperatures between -0.6 ° C to -2 ° C, or average at -1 ° C which initially freezes is free water, followed by bound water, . Freezing starts from the outside, the center of the last freeze. Freezing requires the release of heat from the fish body.
The process, divided into three stages, namely: In the first stage the temperature decreases rapidly until the point of freezing (20o C to 0oC). Then, at the second stage the temperature drops slowly (0 ° C to -5 ° C), for two things: the heat from the fish does not result in a decrease in temperature, but results in freezing of water in the body of the fish and the formation of ice in part Outside of the fish is an obstacle to the cooling process of the parts inside.
In the third stage, if approximately ¾ part of the water content is frozen, the fast running temperature drops back below -5oC. The time required for the fish in freezing to cross the second stage (0oC to -5oC) is called thermal arrest time. Based on the length of this time, the freezing is divided into two, namely quick freezing not more than two hours and slow freezing or sharp freezing for more than two hours.
Rapid freezing and slow freezing affects the size and size of the ice crystals formed. The faster the freeze the smaller the ice crystals are formed, the longer the freezing the larger the ice crystals are formed. Therefore, in slow freezing if melted back then melting crystals will push and damage the composition of the meat network and cause a lot of drip.
Thus, slow freezing produces low quality fish products due to the occurrence of protein denaturation, especially at temperatures of -1oC and -2oC. Clotting is the process of decreasing the temperature of foodstuffs to frozen foodstuffs, ie when the temperatures on the inside are the highest around – 18 o C, although generally the frozen product has a temperature lower than this.
In these frozen temperatures the food is preserved because the microbes can not grow and the enzymes are inactive. In the conduct of freezing, whether done in the sea (ship) or conducted on the ground (company / plant preservation fish), the ordinance is not different. The process of initial execution is to separate the fish according to its size. Thus, between small, medium and large fish are not mixed together.
Fish blocks must have a certain size and shape. The labeling system or color codes shall be carried out at the time containing the materials to assist in the identification of the final product. When horizontal freezing is used, the raw material must be packed in a freezer or other device to obtain uniform blocks of fish. When a vertical plate freezer is used, the raw material must be packed properly between the freezing plate so that there may be less room air. If the fishery product is frozen without wrapping it first, it must be neatly arranged in aluminum pan, or other similar materials.