Local Production of Refrigeration Equipment and Machinery for the Fish Industry
Nazri, M. M., Economic Review
Sea fish or marine fisheries form valuable natural resources of any country. Pakistan has a coastline of about 1050 kilometers and is very rich in fisheries and whose potential is yet to be determined.
In 1990-91, the total fish production was estimated at 455,000 tonnes against 446,000 tomes in 1989-90 and 445,000 tonnes in 1988-89. The following figures of exports illustrate the point:
Year Million $ 1988-89 110 1989-90 95 1990-91 114 1991-92 103 1992-93 165
Fish is perishable among the food which, begins to spoil immediately after death. Since the rate of spoilage depends on the temperature of fish, the spoilage of fish can be reduced if the temperature can be brought down rapidly. The refrigeration plays an important role in fish preservation although there are other methods such as drying, dehydration, curing, irradiation and canning.
The Fisheries Industry in Pakistan has developed as one of the major sources of foreign exchange earner. The most significant is shrimp trawled mostly near Pakistan's coastal water. The frozen shrimp forms major part of export (80 per cent of the total) with 5 per cent canned shrimp.
Chilling of Fish
Preservation of fish by refrigeration comes under the category of two groups:
a) Chilling and b) Freezing
Chilling: The chilling of fish at a temperature of 0 |degrees~ C, that is just above the freezing point of fish, does not spoil completely but checks for some time. There are two methods of chilling, one is chilling with ice and the other is chilling with sea water known as refrigerated sea water (RSW).
Chilling with ice generally practiced in most of the fishing industry. But RSW has not been practiced widely in the fishing industry, though it maintains uniform temperature, causing less damage to fish during heavy catch and larger loading capacity. It has been observed that some bigger imported trawlers have RSW storage facilities which make the better.
Fish Freezing: There are several methods for the freezing of fish such as sharp freezing, plate freezing, air blast freezing by immersion or spray and ultra rapid freezing etc.
There are two types of plate freezing namely:
a) Horizontal plate freezing and b) Vertical plate freezing.
In the first case, freezing is accomplished by refrigerant flowing through connected passage. In the earlier plate freezers on one side of the plates was made to come in contact with the product.
While the vertical plate freezer has been developed for freezing whole fish on board fishing vessels which has not been practiced widely in Pakistan as we are not having larger size of vessels.
Freezing by Immersion
Fish is frozen by using a cold liquid or by spraying. In advance countries this method has been used where big trawlers are employed and where RSW and cold storage facilities are available.
Heat transfer can be rapid even with moderate circulation. In this method heat transfer can be rapid even with moderate circulation because there is good contact with the product. Thus, like air blast freezer, the immersion freezer will accommodate fish of various sizes and shapes but will be more compact and consume less power. In the direct method, the product is immersed or sprayed with a sodium chloride brine. In the indirect method, the product is contained in moulds which makes possible the use of other cooling media such as calcium chloride brine.
Sodium chloride brine can be made up to any desired strength according to the desired freezing point of the brine. A saturate solution which contains about 26 per cent salt, freezes at 21 |degrees~ C. In practice, therefore, the operating temperature cannot be lower than about 19 |degrees~ C. This is a serious limitation because the refrigerant temperature should be below 30 |degrees~ C and storage temperature should be 23 |degrees~ C or lower in most applications. …