12.2 Grading, nutrition and storage

Why fish is good food

Fish and shellfish carry few calories and little fat or sodium. They are high in protein and in vitamins A, B and D, and they supply minerals:

• calcium, above all in canned fish whose bones are eaten;
• phosphorus;
• potassium;
• iron, which mollusks are especially rich in.

Fish are rich in omega-3 fatty acids, a group of polyunsaturated fats that may help against high blood cholesterol and some heart disease. Shellfish carry less cholesterol than people once believed. Crustaceans hold more than mollusks, but both hold far less than red meat or eggs.

The usual ways of cooking fish help too. Broiling, grilling, poaching and steaming add little fat, or none.

Inspection and grades in the United States

In the United States, meat and poultry must be inspected by law, but fish and shellfish inspection is voluntary. The seller pays for it, and the Department of Commerce (USDC) runs it. There are three types:

• Type 1 covers the whole process, from raw fish to finished product, in the plant. Products inspected this way may carry the mark "Packed under Federal Inspection" (PUFI). It means the product is safe, wholesome, correctly labeled, of reasonably good flavor and smell, and made in an official plant.
• Type 2 checks one lot of product in a warehouse, plant or cold store against the buyer's specification: condition, weight, labeling and packaging.
• Type 3 checks sanitation only. Boats and plants that pass go on a published USDC list of approved establishments.

Only fish inspected under Type 1 can be graded, and grading standards exist only for the most common kinds. Grade A is top quality: good flavor and smell, and almost no blemishes. Most fish served in restaurants is Grade A. Grade B is good quality and Grade C fairly good; both mostly end up canned or processed.

Checking freshness yourself

An inspection stamp does not promise good fish. A few hours too warm, or two days in the refrigerator, can ruin it. So check freshness when you buy, and check again just before you cook.

• Smell. The easiest test. Fresh fish smells faintly of the sea, or of nothing. Any off smell, or a smell of ammonia, means the fish is old or was handled badly.
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• Eyes. Clear and full. Sunken eyes mean the fish is drying out.
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• Gills. Whole and bright red. Brown gills mean age.
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• Texture. Firm flesh that springs back when you press it. Soft, mushy flesh that stays dented is old or poor.
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• Fins and scales. Moist and full. Dry ones mean age; torn ones mean rough handling.
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• Cut surfaces. Moist and shiny, with no bruises, dark spots, or brown, dry edges.
• Movement. Buy shellfish alive. Lobsters and crabs should be lively. An open clam, mussel or oyster should close when you tap it; if it does not, it is dead, so throw it out. Geoduck, razor and steamer clams are the exception, because the siphon sticks out and stops the shell from closing. Avoid mollusks with broken shells, or shells so heavy they may be full of mud or sand.
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Market forms

Wholesalers sell fish in several market forms.

Market forms of fish.

Labels also say how the fish was kept:

• Fresh: never frozen.
• Chilled: kept refrigerated, at −1°C to 1°C (30°F to 34°F). Some sellers use it in place of "fresh", which can be vague.
• Flash-frozen: frozen fast, on the boat or at a plant, within hours of the catch. Fresh-frozen is frozen while fresh, but less quickly.
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• Frozen: held at 0°F (−18°C) or colder.
• Glazed: frozen, then dipped in water so a coat of ice guards it against freezer burn.
• Fancy: a trade code that means the fish was frozen before.

Buying shellfish by count

Shellfish are sold live in the shell, shucked (taken out of the shell) or processed. Live and shucked shellfish are usually sold by count, the number of pieces in a unit. The unit depends on the shellfish:

• Standard live Eastern oysters come 200 to 250 to the bushel.
• Shucked Eastern oyster meat comes 350 to the gallon.
• Shrimp and crab legs are often sold by the number per pound.
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• Whole crabs are graded by size.
• Lobsters are sold by weight.

Cutting fish in your own kitchen

Before buying whole fish to cut up yourself, ask four questions:

• Can the kitchen use the bones and trimmings?
• Can the staff cut fillets, steaks and portions well?
• Is there room to store whole fish?
• What is the fish for?

For holding, cutting with and sharpening a knife, see chapter 4: Knife work.

Scaling. Scale any fish that will be cooked with its skin on.

• Hold the fish by the tail and scrape from tail to head with a fish scaler, or with the back of a knife, gently, so you do not bruise the flesh.
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• Turn it over and do the other side.
• Rinse it in cool water.

Pan-dressing a flat fish. Work in this order:

• Cut the head off with a V-shaped cut, and pull it away with the guts.
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• Rinse the cavity clean of blood.
• Snip off the tail and fins with kitchen shears.
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Filleting a round fish. A round fish is filleted from the head end:

• Cut behind the gills down to the backbone, leaving the head on.
• Turn the knife toward the tail and cut along the backbone in long, smooth strokes. Keep the blade against the bone so no flesh is wasted; you will feel it pass through the small pin bones.
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• Free the fillet, turn the fish, and do the other side.
• Trim the rib bones off each fillet with a flexible boning knife.
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Filleting a flat fish. A flat fish gives four fillets: two large ones from the top and two smaller ones from the bottom. Scale first if the skin stays on, since scaling is easier on a whole fish; skip it if the skin comes off.

• Lay the fish dark side up and run the tip of a flexible boning knife down the backbone from head to tail.
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• Slide the blade between the flesh and the ribs, keeping it on the bone, and lift off each fillet.
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• Turn the fish and repeat.
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Skinning. Dover sole is the one flat fish whose skin pulls off whole: cut across the skin just in front of the tail, grip it with a towel, and pull it toward the head. Flounder, petrale and other soles are too delicate for that; fillet them first. To skin any fillet, lay it skin side down, start at the tail, and slide a knife between flesh and skin with a sawing motion, the blade angled down toward the skin while you hold the skin tight.

Pin bones. A round fish fillet has a line of small bones inside the flesh along its length. They are usually cut out. In salmon, pull them one by one with salmon tweezers or needle-nose pliers, finding each with your fingertips, starting at the head end.

Storing fresh fish

Temperature matters more than anything else in keeping fish. All cold food is kept at 4°C (40°F) or colder. Fresh seafood needs more: pack it in ice, keep it at −1°C to 2°C, and use it as soon as you can. Fish kept at 41°F (5°C) lasts about half as long as fish kept at 32°F (0°C).

Fish usually arrives packed in ice. Get it onto ice in the refrigerator quickly:

• Bury whole fish in shaved or crushed ice, in a perforated pan so the meltwater drains away. With only cubed ice, put the cubes in plastic bags and set them gently on the fish so they do not dent or bruise it.
• Wrap cut and portioned fish in moisture-proof packaging before icing, so water does not spoil the cut flesh.
• Set fillets in plastic trays, fresh scallops, and shucked oysters and clams on ice or pack ice around them, but never let the ice touch the flesh.
• Drain and re-ice the fish every day.
• Store raw seafood on the lower shelves, below anything cooked or ready to eat.
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Keeping shellfish alive

Live clams, mussels and oysters stay in the boxes or net bags they came in, in high humidity. Never seal them in plastic bags, and never ice them. Kept well, they stay alive for up to a week. Like all food in cold storage, they are kept at 4°C (40°F) or colder.

Without a saltwater tank, keep live lobsters, crabs and other crustaceans in boxes with seaweed or damp newspaper. Most of them pass salt water over their gills, so ice or fresh water kills them. Kept well, lobsters and crabs live for several days.

Frozen fish

Frozen food is stored at −18°C (0°F) or colder, and fish kept colder still lasts much longer. If the freezer warms past −18°C, food loses color and vitamins, and cooling it again does not undo that. Wrap fish well, or freezer burn will dry out its surface, and use the oldest stock first.

Thaw frozen fish in the refrigerator. Once it has thawed, treat it as fresh fish.

Knowing when fish is done

One long-standing guide allows 10 minutes for each inch (2.5 centimeters) of thickness, whatever the method. That is a fair rule of thumb, but in a professional kitchen it is better to judge by the fish itself:

• It turns opaque. Raw fish looks a little see-through. As its proteins set, it turns solid in color.
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• It firms up. Press it with a finger. Raw fish is soft; cooked fish pushes back and springs up quickly.
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• It comes off the bone. Raw flesh clings to the bones; cooked flesh lifts away easily.
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• It starts to flake. As the thin connective tissue breaks down, the bundles of muscle fiber begin to part. Fish is done when it just begins to flake; fish that flakes easily is overdone and dry.
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The food safety test is different: cook fish until it flakes easily. There is a temperature too. Fish must reach 70°C (158°F) inside, and mixed dishes containing fish 74°C (165°F), held there for 15 seconds or more. Check with a thermometer rather than trusting the clock.

Fish keeps cooking for a short time after it leaves the heat. This is carryover cooking. see chapter 8: Carryover cooking So take fish off the heat a little early and let the stored heat finish it.