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Curing reduces water activity through the addition of chemicals, such as salt, sugars, or acids. There are two main types of salt-curing used in the fish industry: dry salting and pickle-curing. In dry salting the butchered fish is split along the backbone and buried in salt (called a wet stack). Brine is drained off until the water content of the flesh is reduced to approximately 50 percent (the typical water content of fresh fish is 75 to 80 percent) and the salt content approaches 25 percent. In heavy or hard-cure salting, an additional step is taken in which warm air is forced over the surface of the fish until the water content is reduced to about 20 percent and the salt content is increased to approximately 30 percent. Most dry-salted fish products are consumed in warm, humid countries or in areas that have few means of holding products in refrigeration or cold storage.

In pickle-curing, fish are preserved in airtight barrels in a strong pickle solution formed by the dissolving of salt in the body fluids. This curing method is used for fatty fish such as herring.

Smoking

Traditionally, smoking was a combination of drying and adding chemicals from the smoke to the fish, thus preserving and adding flavour to the final product. However, much of the fish smoked today is exposed to smoke just long enough to provide the desired flavour with little, if any, drying. These products, called kippered fish, have short shelf lives, even under refrigeration, since the water activity remains high enough for spoilage organisms to grow.

The smoking process consists of soaking butchered fish in a 70 to 80 percent brine solution for a few hours to overnight, resulting in a 2 to 3 percent salt content in the fish. The fish are then partially dried on racks. As the brine on the surface dries, dissolved proteins produce a glossy appearance, which is one of the commercial criteria for quality. Smoking is carried out in kilns or forced-air smokehouses that expose the fish to smoke from smoldering wood or sawdust. In cold-smoking the temperature does not exceed 29 °C (85 °F), and the fish is not cooked during the process. Hot-smoking is more common and is designed to cook the fish as well as to smoke it.

Irradiating

Irradiation offers a means of pasteurizing or sterilizing a variety of food products. However, the use of this process has not been universally accepted throughout the food industry.

Food irradiators utilize radioisotopes, such as cobalt-60 (60Co) or cesium-137 (137Cs), or electron beam generators to provide a source of ionizing radiation. The irradiation of seafood has been extensively studied since the 1950s. The pasteurization of fresh fish using low-level dosages of ionizing radiation may extend the shelf life of the product up to several weeks. The sensory and nutritional characteristics of the fish are unaffected at these low levels of radiation.

Total utilization of raw materials

In response to an increased demand for “ready-to-eat” fish products, along with a growing awareness of the limited supply of natural fish stocks, the fish industry has developed procedures for more efficient utilization of available raw materials. Because as much as 70 percent of harvested fish has traditionally been discarded or converted into cheap animal feeds, initial efforts to conserve fishery resources have focused on the development of edible products from underutilized species.

Surimi

Surimi was developed in Japan several centuries ago when it was discovered that washing minced fish flesh, followed by heating, resulted in a natural gelling of the flesh. When the surimi was combined with other ingredients, mixed or kneaded, and steamed, various fish gel products called kamaboko (fish cakes) were produced and sold as neriseihin (kneaded seafoods).

Modern surimi production consists of continuous operating lines with automated machinery for heading, gutting, and deboning of the fish; mincing, washing, and pressing (to remove water); and heating of the flesh. The surimi is then mixed with cryoprotectants and frozen for cold storage. Frozen surimi blocks are shipped to processing plants that produce various kamaboko products such as original kamaboko (itatsuki), broiled kamaboko (chikuwa), fried kamaboko (satsumage), and analog products, including imitation crab, scallops, and shrimp.

The chemistry of the surimi process involves the differential extraction of muscle proteins. The water-soluble sarcoplasmic proteins are removed during the washing of the minced flesh. These proteins inhibit the gelling properties of the minced flesh. The flesh is then comminuted with salt, which solubilizes the myofibrillar proteins actin and myosin. Upon heating, the myofibrillar proteins form a network structure that takes on a gellike consistency. Cryoprotectants are necessary to stabilize the myofibrillar protein network during frozen storage.

Minced fish flesh

The success of surimi-based products has stimulated the development of other products made from minced flesh. Minced fish products do not undergo the repeated washing cycles necessary for the production of surimi. Because of the presence of residual oils and sarcoplasmic enzymes (both oil and sarcoplasmic proteins are removed during the washing of surimi), cryoprotectants must also be added to the minced flesh prior to freezing in order to protect the product from oil oxidation and enzyme degradation.

Minced fish flesh is used in a wide variety of products. The largest volumes are extruded into formed patties for main dishes and sandwiches. The forming process involves combining the minced flesh with condiments and extruding the mix under pressure to produce the desired product, much like the formation of hamburger patties and sausages. The formed product may be battered and breaded in a final processing step. Other minced flesh products include nuggets and items used as hors d’oeuvres, fish chowders, and smoked fish sticks.

George M. Pigott

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seafood, edible aquatic animals, excluding mammals, but including both freshwater and ocean creatures. Most nontoxic aquatic species are exploited for food by humans. Even those with toxic properties, such as certain blowfish, can be prepared so as to circumvent harm to the consumer.

Fish and other seafood may be humanity’s most important food, after cereals, furnishing about 15 percent of the world population’s protein intake. Lean fish muscle provides 18–25 percent protein by weight, the equivalent of beef or poultry, but is much lower in calories. In fish one gram of protein is present for 4 to 10 calories, as contrasted with 10–20 calories per protein gram for lean meats and up to 30 for fatty meats.

Seafood comprises all bony fishes and the more primitive sharks, skates, rays, sawfish, sturgeons, and lampreys; crustaceans such as lobsters, crabs, shrimps, prawns, and crayfish; mollusks, including clams, oysters, cockles, mussels, periwinkles, whelks, snails, abalones, scallops, and limpets; the cephalopod mollusks—squids, octopuses, and cuttlefish; edible jellyfish; sea turtles; frogs; and two echinoderms—sea urchins and sea cucumbers.

Chef tossing vegetables in a frying pan over a burner (skillet, food).
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The most commercially important ocean fish are species of salmon, herring, codfish, flatfish (flounder, sole, halibut, turbot), redfish (ocean perch), jack mackerel, tuna, mackerel, and sardine. Major species of freshwater fish are carp, eel, trout, whitefish, pike, pike perch, and catfish. The catch ranges in size from whitebait and baby eels, both about 5 cm (2 inches) long, to bluefin tuna, up to 4.3 metres (14 feet) in length.

Because fish spoils quickly and is thus highly perishable, for most of history the majority of the catch has been dried, smoked, salted, pickled, or fermented when not eaten fresh. Even when these practices are no longer strictly necessary for preservation, the distinctive alterations in taste that they produce have cultivated a continuing demand for fish preserved in these ways.

Fish are cooked whole or cut into steaks, fillets, or chunks. Crustaceans are usually cooked whole, alive, as are most mollusks. Larger, tougher mollusks are ground or sliced and pounded to tenderize the tough flesh. Much seafood is eaten uncooked, either completely raw or somewhat modified by marination.

In addition to flesh, the roe of fishes and some shellfish and the eggs of turtles are eaten. Caviar, the roe of sturgeon, is now synonymous with luxury but was relatively cheap and common until the latter part of the 19th century, when worldwide sturgeon stocks began to decline rapidly.

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A major consideration in cooking fish or shellfish is to avoid overcooking. The rule of thumb is that fish should be cooked 10 minutes per inch, measured through the thickest part of the fish, with an additional 5 minutes required if the fish is cooked in a sauce. The time should be doubled for frozen fish.

The repertory of fish cookery worldwide is immense. Fish may be poached, sautéed, broiled, baked, deep-fried, steamed, or eaten raw. Seafood, often in combination, forms the basis of many savoury stews, soups, chowders, gumbos, and bisques. In general, the more delicate and lean seafoods are prepared with milder seasonings and sauces, while those that are more robust in flavour, with coarser or fattier flesh, receive more pronounced seasoning.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Kara Rogers.