Why freeze at Sea?
Some facts about freezing
How to handle sea-frozen fish
Everyone who handles fish landed from the big distant-water trawlers knows that it is not always fresh. Some of it is even condemned before the auction or is sold as pet food. This is not the fault of the trawlermen. The trouble is that nowadays, with many European nations fishing in Arctic waters, catching fish is slower and more difficult. The days of short trips are gone.
... it is not always fresh...
... will warm up very quickly...
Unfortunately, even when stowed in ice, cod and the like will not keep in first-class condition for more than a week or so. And it is condemnable after 14 to 16 days.
Fish, if it is absolutely fresh, properly frozen and cold-stored, will however keep in good condition for many months. The development of trawlers able to freeze the early part, or the whole of their catches at sea is largely the outcome of British research and development. The method promises to provide fresher quality fish from more distant areas, and will allow trawlers to operate more economically by enabling them to remain longer on the fishing grounds.
These developments will benefit everyone connected with the fishing industry not only on the catching side, but on the landing, processing and distribution side as well.
If sea-frozen fish is to be acceptable it must be possible to use it like ordinary wet fish. When thawed, it should be suitable for filleting and smoking, for example. Unfortunately, freezing and cold storage can cause some changes in the appearance and texture of the thawed fish, but if the job has been done properly, these changes are slight and would certainly pass unnoticed by the consumer. If freezing and cold storage has been badly done, however, the changes in gloss, colour and texture are obvious and the flavour also suffers.
Scientists at the Torry Research Station have found how these changes can be kept in check. The fish must be quick-frozen, and special equipment has been designed at Torry for performing this difficult operation at sea. The frozen fish must then be kept at the really low temperature of minus 20°F (52 degrees of frost) right up to the moment it is thawed for use. When it is realised that the holds of the best large refrigerated-cargo vessels are designed to operate only at 0°F to minus 5°F, it will be seen that to provide a refrigerated hold able to operate at minus 20°F is an exacting requirement, especially in a much smaller vessel like a trawler. Nevertheless, it has been done.
Freezing at sea is a new development that offers prosperity and a bright future for the entire fish industry. But the success of the whole venture at the present time depends on whether or not the industry and the consumer find the product satisfactory, and this largely depends on proper handling of the frozen blocks once they are unloaded from the trawler's cold-store.
What can cause loss of quality? Briefly, warming up of the blocks, initially at minus 20°F, and rough treatment of both frozen blocks and of the fish during thawing.
Frozen blocks of fish will warm up very quickly if they are left lying on the quayside after discharge from the trawler. Although they may still appear to be hard frozen, they may only be a few degrees below melting ice temperature. And it is not easy to get them down to minus 20°F again and as a result, quality will suffer. Special equipment running at temperatures much lower than minus 20°F is required on board the trawler to freeze the fish rapidly to storage temperature; it is not sufficient just to put the fish into the cold store, even if this is itself running at a low temperature. Cold stores on shore will not have equipment of this kind. It will take weeks therefore to cool down in cold store an average cargo of sea-frozen fish that has been allowed to warm up on the quayside - by which time much of it will be spoilt. It will look rather poor when it is thawed and it will not produce a good smoked product or taste very nice.
... some slight rise in temperature is unavoidable...
... frozen fish... are quite brittle...
Blocks of frozen fish must therefore be handled quickly out of and into cold store - they must not be left lying about in the open. And since some slight rise in temperature is unavoidable however quickly the operation is carried out, blocks should only be transferred from one store to another when this is absolutely necessary. Blocks should be rapidly removed from the cold store on the trawler to that on shore, where they should remain until thawed for processing.
Although speedy handling is the essence of the matter, rough handling must be avoided. Blocks of sea-frozen fish will readily break up, and a lot of broken blocks in a batch makes later handling more difficult. Also, frozen fish when really cold, as they should be, are quite brittle; if blocks offish are chucked about, tails and fins will snap off and eyes will be broken, or whole fish themselves may break in half.
Some of the damage that can be caused by rough handling is not obvious until the block is thawed. If blocks are slid over wooden or concrete floors, or if somebody stands on a block in his hobnailed boots - and this does sometimes happen - the skin will be damaged. When thawed, the fish lack gloss and look as if they have been dragged along the market floor.
The best way to unload the frozen cargo would be to transfer the blocks direct to a cold store by conveyor belt. Unfortunately, not many cold stores are conveniently sited at the quayside. Perhaps the next best way is to stack the blocks quickly and carefully on wooden or metal bins or pallets and rapidly remove them to the cold store, preferably on a pre-cooled insulated lorry. Once the fish are loaded into the bins or pallets they should remain there, in the store, until needed for thawing and processing, thus avoiding further handling.
Frozen blocks of sea-frozen fish can be satisfactorily thawed in a dielectric or air-blast thawer; but here again careless handling both into and out of the thawer can spoil appearance and eating quality. When frozen fish are almost thawed, the flesh can be easily torn, for example, by somebody tearing fish apart or squeezing single fish to see if they are thawed or not.
The thawed fish, like fresh fish should be handled with some care. They should not be stacked in large heaps - especially the fillets - nor should kits containing fish be stacked one within another.
... stands on a block in his hobnailed boots...
Scientists have shown that freezing at sea can help to bring much better quality fish to the port with ultimate benefit to the consumer. Whether it reaches the housewife in good condition depends on how carefully it is handled at the port.
If care is taken along the lines discussed above, then all those connected with the distant-water industry can share in the benefits to be obtained from this new method of bringing back distant-water fish in prime condition. There is no reason why the trawler fleet of the future should not be composed entirely of freezer trawlers - fishing not only their traditional grounds but new and more distant areas.
But success or failure of the venture depends very largely on
the care of the shore-handling side of the business.
