|Small-Scale Processing of Fish (ILO - WEP, 1982, 140 p.)|
|CHAPTER IV. THERMAL PROCESSING|
Certain fish are not suitable for canning. For example, the integral cooking operation tends to break up the flesh of white fish before softening the bones, thus making these unsuitable for canning. Fish with a high oil content (mainly pelagic species, e.g. herring, mackerel, tuna and sardine) have much firmer flesh and softer bones after cooking, and may thus maintain their original shapes. A further advantage in canning oily fish is that this method provies protection from oxidation and rancidity development, a feature which is not provided by the simpler curing operations.
Fish quality is of the utmost importance in canning, and good post-harvest handling, including the use of ice, refrigerated sea water or freezing immediately after capture is required. Capture itself also demands speed. For example, methods such as gill netting, which can lead to advanced spoilage in the warm water prior to landing, are not as effective as purse seining where large numbers of fish can be encircled and landed in a short period of time. Oily species of fish tend to deteriorate faster than non-oily species, a particular common feature being the burst abdomen, which is indicative of spoilage. The need for high quality raw materials in large amounts requires the use of large motorised vessels with sufficient space for adequate chill or frozen storage, and fast enough to return to port before spoilage can take place. The proper use of ice is important. Sufficient quantities of flake ice, well mixed in with the fish reduces the temperature of the fish much faster than crushed block ice which may bruise or otherwise damage the fish. The provision of proper landing facilities (e.g. harbour/ice plants, etc.) is necessary if fish are to be delivered in good condition to the processing plant.
In order for the plant to operate efficiently, a regular and large supply of fish is required. Pelagic fisheries are often seasonal and, if other products cannot be canned during the off-season, the plant may have to shut down. For example, on the Mexican Pacific coast, the sardines are only available for a few months and the cannery is closed for the rest of the year.
Conversely, if fish catches are very large, this may present throughput processing problems in the plant and the use of either cold or chilled stores as buffer storage zones may be necessary.
It is also important to take account of the market demand for specific kinds of fish. It has been found in the past that tuna and tuna-like fish, sardines and sardine-like fish, crustaceans, and especially shrimp, and molluscs, are the most profitable types of fishery products used in canning (Da Costa, 1973).