How to Conserve Fish and Stop Degradation

Fish degradation

From the time of capture to its food use, fresh fish must necessarily be refrigerated; the conservation of the catch in ice at 0 ° C (constant temperature) does not alter its composition for about 4 to 7 days.

After 7 - 10 days (first if the temperature is above 0 ° C or undergoes important fluctuations as it happens when it is exposed in the market stalls) the first important alterations begin; initially, we are witnessing the transformation of triethylamine oxide into trimethylamine and then into dimethylamine, by the bacterial and OWN enzymes of the meat.

Over time the irreversible reaction leads to the formation of monoethylamine and formaldehyde (responsible for the typical smell of damaged fish) release of sulphidric acid (which contributes to the formation of a nauseating aroma) and of biogenic amines (histamine, tryptamine, cadaverine, putrescine, tyramine).

NB . Histamine is already present in discrete quantities in fresh fish and the increase in its concentration can give rise to pseudo-allergic reactions in hypersensitive subjects (appearance of red dots on the skin, nausea, abdominal pain, etc.), similarly to the ingestion of strawberries when it exists. a subjective predisposition.

In addition to chemical transformations, fish can be affected by microbiological contamination, especially of bacteria: Pseudomonas, Moraxella and Flavobacterium-Cytophage .

How to preserve it?

Preserving fish appropriately is a very important aspect both from a hygienic, taste and economic point of view (reduction of waste due to poor storage).

Fish and all fishery products (molluscs and crustaceans) are highly perishable due to the high intake of polyunsaturated fatty acids (PUFA), the high concentration of free amino acids and nitrogen groups, and the high concentration of OWN proteolytic enzymes . In addition, any microbial load (bivalve molluscs and flat or bottom fish), viral (bivalve molluscs) and parasites (all fish), in the absence of adequate conservation, increases exponentially, increasing the risk of parasitosis, poisoning, infections or food poisoning.

Fish can be preserved in many ways, some of which are ancient or traditional and others innovative or technological.

Refrigeration

On the fishing boats, the fish caught is immediately subjected to a first treatment called icing, or the covering of the product with crushed ice; alternatively it is gutted, washed with sea water and stored at -2 ° C to freeze the superficial parts. On-board refrigeration allows fresh fish to be kept for a total of 14 days (from picking to the table).

Homemade or catering refrigeration is based on a few simple steps: removal from the container, washing, possible evisceration, re-washing, placement in polyethylene basins with perforated grids for draining and ice cover. and storage at 0 ° C. Preservation potential at home: 2-3 days.

freezing

It is a preservation method that lowers the food temperature to -20 ° C or -30 ° C. Slow freezing or freezing causes water molecules to aggregate to form ice macrocrystals; it is mainly used for large fish and is performed using cold storage rooms that reach -50 ° C or -60 ° C or by means of freezing tunnels that exploit liquid nitrogen at -60 ° C.

Homemade preservation of frozen fish takes place in cockpit or cupboard freezers.

Freezing

It is a preservation method that lowers the temperature so quickly that it does not allow the formation of ice macrocrystals; in their place very small crystals are formed. In this way, compared to freezing, in the de-icing of the fish the cellular rupture and the relative release of the organic liquids is reduced to a minimum. This storage is obtained by using forced air at -40 ° C and the product must reach -18 ° C within 4 hours; it can only be performed in centers authorized by the USSL.

Frozen fish must be kept at a transport temperature not <-18 ° C and without interrupting the cold chain.

Boxing

It is a preservation technique useful especially for small fish such as sardines and anchovies, but also for mackerel, salmon, tuna and some molluscs such as mussels and clams.

The fish to be canned must be fresh, clean, washed in brine, cut, placed in boxes, covered with a preservative and kept at + 70 ° C; subsequently, the boxes are sealed with a lid, sterilized at 120 ° C quickly and cooled just as quickly.

Home or catering conservation must take place according to the indications mentioned on the label.

SMOKING

It is a fish preservation technique typical of Northern Europe that has very ancient origins; it is based on the display of pieces of fish, or small whole fish, against the smoke obtained from the combustion of wood.

The fish must first be cleaned, washed and stored (minutes or hours) in smoke-saturated chambers obtained from birch, pear, chestnut or oak, which aromatizes and dehydrates the food, further promoting its preservation by penetration of the aromatic substances (increase of polycyclic aromatic hydrocarbons).

Smoking is mainly used for the storage of trout, salmon, herring and eels, generally consumed as hors d'oeuvres.

Dry salting

Dry salting is also a very ancient preservation method that exploits the osmotic power of coarse salt on meat. It is applied essentially to the species: cod, herring and anchovy. Dry salting can be started directly on the fishing boat or later, after disembarking, but in any case after evisceration, washing and filleting.

To reduce the humidity of the food to no more than 40%, dry salting requires numerous checks and different processes useful for removing liquids from the fish tissue and replacing the covering salt.

Salted in stew

It is a fast storage method; it consists in placing the fish in ceramic containers, inside which they are covered with a 15-30% aqueous solution of sodium chloride; the salting in stew must be maintained for some days and ends with the drying of the fish that reaches a total humidity of 40%.

Drying

Like smoking, drying is also an ancient technique of preserving fish (cod) used mainly in the Nordic countries; traditionally, the fish should be cleaned, gutted, washed, boned, dried and left hanging on special trellises in the sun for several months, until it reaches a woody consistency (typical of stockfish) . On an industrial level, cod is exposed for 2-3 months to hot air currents which cause the reduction of humidity in the meat up to 14%.

Before consumption, the dried fish should be made more "elastic" by beating with a wooden hammer or by passing it under special crushing rollers; subsequently, it is necessary to rehydrate it after soaking 2-3 days in running water.

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