Fish Preservation Techniques
- A large section of the Indian population uses fish as food. All over the world, fish and fish products are consumed by people.
- Fish is an easily available source of protein. It is highly nutritious and easily digestible. In India, edible fishes are abundantly available from sea, rivers, lakes, ponds and marshes. Fish is also an item of export trade.
- Fish body contains proteins, fats, minerals, vitamins, amino acids, iodine, phosphorus and large amount of water.
- Thereafter dead fishes get spoiled by the process of decomposition and hence proper fish preservation techniques or methods are essential.
- Moreover, fishes are also provided with a variety of bacteria which immediately attack on the various body constituents of fish after death.
- In this light, preservation of fishes is an essential process. There are several different methods or techniques generally practiced in our country as well as abroad for fish preservation.
Following methods are used in fish preservation.
1. Chilling or refrigeration:
In this method, the basic idea is to preserve the fish at 0°C which prevents the spoilage for short period. At this temperature, the rate of decomposition of body tissue is drastically reduced and fish is preserved. For this purpose, ice is the best material used. Alternate layers of fish and ice are kept in closed vessels to maintain the temperature at 0°C. Sometimes for the preservation of large sized fishes, the ice pieces or cubes are also kept in the abdominal cavity of gutted fishes. This is cheaper and convenient method of fish preservation and widely used for fish transport from one place to another of short distance.
2. Deep freezing:
This method of fish preservation is used for large periods of preservation. It is more effective but costly process. Before freezing, fishes are washed properly and kept at a temperature of -18°C for longer period. For this process, only the fresh fish in good condition are deep frozen. Prior to keep the fish in this process the heads of large fishes are removed and they are also gutted and washed. This process is without spoilage and fishes can be kept for a longer period.
3. Freeze drying:
This process is lengthy as well as expensive and used for the preservation of only good quality of fishes. This process involves two steps, first freezing of the fish and then the second step is drying of fish by sublimation. In this technique ice is changed into water vapour without melting. By this process the colour and nutritive substances are completely preserved. In this technique the fish is frozen at -20°C by keeping them in freezing chamber. As soon as freezing is over, the frozen fishes are kept in trays and are transferred to the cabin containing horizontal heating plates for drying in vacuum. The fishes are well dried due to hot plates and then they are placed in air conditioned chamber.
Salting is very old and common practice used in fish preservation in India and other parts of the world. Salting is nothing but the partial dehydration of fishes by osmosis with sodium chloride. Due to intense salting, microbes are killed and diastasis is stopped. In this process before salting, the heads of the fishes are removed, gutted and washed and then salted as soon as possible. There are different methods of salting such as dry salting, cold salting, light or strong salting.
(a) Dry salting: In this method, alternate layers of fish and salt are placed. This is called dry salting.
(b) Wet salting or brine: In this process, the fishes are dipped in salty water called brine. The brine or salt water is used of two different concentrations. In light brine salt concentration is 16% and strong brine is used containing 25% salt. After this salt water treatment the fishes are dipped in salt.
5. Cold salting:
In this process, salt and crushed ice is spread on the fishes. This process is carried out in cold room only where temperature is maintained at 2 or 3°C. This is also called light cold salting.
Strong salting process is performed at the normal room temperature. Salting is very common practice adopted by fishermen near sea shores. The small sized fishes are sun dried and preserved for longer period.
This is also a very old and common practice of fish preservation adopted by tropical countries like India, Japan, China and others where sun rays are very powerful to dry the fishes easily. Sunlight is the cheapest and abundant source of heat energy used for drying purpose. By this method small sized fishes are dried. The fishes are kept for dehydration on a mat or anything for 3 to 5 days and during this period turning over the fishes is continued. After complete dehydration, the dry fishes can be stored. These dried fishes are also used for making fish fertilizer. The larger fishes are cut into pieces for easy drying. However, this method is not perfect for longer preservation.
(i) Sun curing: It is a little bit advanced method over simple sun drying in which body of fish is opened from the ventral side and viscera and gills are removed. Then the fish is washed and salted in ratio of 1: 3 to 1: 8 (salt : fish} which is related with the size of fish.
(ii) Mona curing: It is similar to sun curing but difference is that no incision is made in the body of the fish to remove the intestine and gills. These organs are directly removed from mouth. Further, such eviscerated fishes are cleaned, salted and dried as earlier.
(iii) Wet curing: It is also like sun curing with the only difference in the packing of salted fish as such. This method is used only for fatty fishes.
Canning is expensive process of fish preservation and hence it is not commonly used. However, it is widely used in advanced countries like America, France, Japan and Spain. This is lengthy, complicated but very advanced process of preservation. In this process, the best quality fishes are selected and their heads and viscera are removed. Then these eviscerated fishes are treated with brine (salt water), washed, dried and cooked in olive oil. This process is used to remove excess of water for 2 to 5 minutes. Then the cooked fishes are packed in olive oil in tins and sealed and sent to markets.
The process in which fishes are preserved by the treatment of wood smoke is called as smoking. This permits the preparation of delicate specialities. While using this method the temperature of smoke and its rate of circulation should be controlled. Smoking is again of two types; hot smoking and cold smoking. For cold smoking fishes are dried, salted, exposed to the smokeless fire (38°C) and then processed for real smoke at 28°C.
For the hot smoking process, fresh fishes are used and fishes are subjected at 130°C on strong fire which is followed by smoking at 40°C. The industrial smoking is done in galleries with a smoking installation and a system for the proper circulation of smokes. This method was used to preserve the fishes in World War II but it is not recommended in the present day fish industries.