Canning and Fish Packaging Technology

Unit 3 - Unit operations in canning

3.2.1.5.Precooking
Precooking is done to remove excess moisture and fat from the fish. This can be achieved by steaming, frying and blanching. By this method the fish becomes firm and also the moisture content comes down. After precooking, fish meat looks bright and more attractive. However, there will be some loss of taste and flavour components.

Precooking by steaming is done in retort for 30-45 minutes which expels moisture and fat and can be removed by draining.

Frying is done using refined vegetable oil at a temperature of 160 to 180oC for one to three minutes. Frying results in reduction in moisture, firming of texture, reduction in size and improvement in taste and flavour.

Blanching is one of the precooking methods where the fish/shrimp is dipped in boiling brine containing 6-8% salt for 4-6 minutes. Use of citric acid in blanching of shrimp is a normal practice to achieve better colouration and texture. Blanching results in contraction and curling of shrimp, reduced moisture content, development of firm texture and attractive colouring. Blanching of shrimp helps in controlling the net weight of shrimp in the processed cans.

Live clams, green mussel, oysters and crab are washed, steam cooked for a few minutes to open the shell and to collect the edible portion. It is essential to remove blood from crab meat which otherwise results in blue discolouration.

In tuna, the precooking operation helps in easy separation of dark and light meat. The dark meat is not packed in can as they are not appealing and normally goes for pet food preparations.