What are the ways to select shellfish?

Abalone.
Abalone is expensive because the supply is limited. These large mollusks are found mostly in the waters off California and northern Mexico. Unlike the other mollusks discussed, abalone have only one shell. Most of the animal consists of a massive, muscular foot. Only abalone with meat weighing at least 1/4. pound may be legally harvested; some extremely large abalone yield as much as 3 pounds. The strict regulations governing the harvesting of wild abalone have led to farm-raised abalone, which are largely harvested in California and Hawaii.

Lobsters.
Lobsters are the largest of the crustaceans. They are mainly purchased as Northern (or Maine) lobster, or spiny or rock lobster varieties. Gourmet cooks prefer the female lobster for its finer flavor and because it contains "coral," or lobster roe, which is considered a delicacy When cooked, the roe turns from dark green to red and is often used to color a sauce or served alone as a garnish. Another delicacy, found in both male and female lobsters, is the pale green liver, known as tomalley.

The majority of the meat from a lobster is in the tail, but there is also some in the claws of the Maine lobster. Lobsters are right-handed or left-handed, as indicated by which claw is the larger, and although the larger claw has more meat, that from the smaller claw is sweeter and more tender. Northern lobsters with one or both claws missing are sometimes sold as "culls." They are less expensive and attractive to the buyer interested only in the tail meat. Unless they are canned or frozen, lobsters must remain alive until cooked, at which point their natural dark blue-gray or greenish color turns deep orange or red.

Shrimp.
The tail harbors most of the meat in shrimp. They are sold, headless, in either the raw shell-on (green shrimp), cooked shell-on, or cooked and peeled form. All three forms come both fresh and frozen, but the majority of shrimp are frozen. When shrimp are bought in their shells, they must first be peeled. The next step, if the shrimp are medium or large, is to devein them, which involves removing the dark-colored "sand vein" or intestine that runs along the shrimp's back. The "sand vein" is usually left in small shrimp, where it is undetectable and does not contribute to a gritty, muddy taste. After cleaning, the shrimp are dried by pressing them between paper towels to absorb as much moisture as possible. Before they are cooked, shrimp are somewhat grayish green, but they turn dark pink to borderline red when heated.

Shrimp are available in small, medium, large medium, large, and jumbo sizes. They are purchased according to "count per pound," which varies depending on the region, but obviously the smaller the shrimp, the higher the count per pound. Serving size averages 1/3 to 1/2 pound for headless, unpeeled shrimp or 1/4 to 1/3 pound for peeled and deveined shrimp. The largest jumbo-sized shrimp are frequently misnamed prawns, but true prawns have lobster-like pincer claws and are otherwise different from shrimp. Another shrimp-related North American misnomer is the use of the word scampi for describing large broiled shrimp seasoned with butter and garlic.

Canned Shrimp.
Glass-like beads are sometimes found in canned shrimp, but they are completely harmless. They are formed during canning, specifically under the high heats of sterilization. Called struvite crystals, they consist of magnesium-ammonium phosphate compounds that form when the magnesium from sea water combines with the ammonia that is produced during heating of the shellfish's natural protein. Phosphate treatment prevents struvite crystal formation due to the phosphates binding with the magnesium. Struvite crystals can be crushed to a powder by a fingernail or dissolved by boiling for a few minutes in the weak acid of lemon juice or vinegar.

Crab.
The majority of meat in a crab is found in its claws and legs. The four top commercially harvested crabs are the blue crab from the Atlantic and Gulf coasts, stone crabs from Florida, Dungeness crabs from the Pacific coast, and, most expensive, king crabs from the northern Pacific waters. Soft-shelled blue crabs are considered a delicacy, particularly on the east coast. These crabs are caught while molting, a process during which they shed their shell and have a soft exterior until the new surface is completely hardened. The process may take several days, during which time the crab is more vulnerable to predators, especially two-legged ones such as birds and humans.

Canned Crab.
Canned crab may have a blue tint. This is caused by copper in the crab's blood combining with the ammonia in its flesh. Although the color may appear unappetizing, it is completely harmless.

Crayfish.
Either referred to as crawdads, crayfish, or crawfish, these small crustaceans average 4 ounces in weight. Crayfish looks similar to lobsters but however, they are smaller, and their first pair of walking legs do not develop into huge, flesh-rich claws. Only their tails serve as a source of meat. They are found mainly as a food source in freshwater streams and ponds of the southeastern United States, especially Louisiana. Crayfish are sold both head-on and tails only, fresh and frozen.