The purchaser of shellfish is faced with a number of
different forms from which to choose. The first decision is whether to
buy them processed or alive. Lobsters, crabs. oysters, and clams all may
be purchased alive and in their shells. Shellfish are highly perishable,
and to maintain their quality, must be kept alive until they are cooked,
or in the case of oysters, occasionally consumed raw. Crustaceans being
normally active creatures, it is easy to tell whether or not they are
alive, but determining the state of mollusks in their closed shells
poses more of a puzzle. Tapping on the shell should cause it to close
more tightly; the rule in most cases is that if the shell remains open,
the mollusk is dead and should be discarded. The exceptions to this rule
are mussels, which ordinarily gape, and longneck (steamer or soft-shell)
clams, which normally have a gap in the shells where the "neck"
protrudes. Any shells that are broken, have a decaying odor, or float
should be discarded. An old rule of thumb held that shellfish should be
eaten only during the months with the letter "r" in their names, because
bacterial illnesses are more common in the warmer months of May through
This is still a valid guideline, although modern methods of harvesting
and storage provide a safer supply of shellfish year round.
Shellfish can also be bought cooked in the shell and chilled or frozen.
Alternatively, the meat can be removed from the shell and sold fresh,
chilled, frozen, canned, salted, smoked, or dried. Uncooked shellfish
can be sold headless, as in the case of shrimp or lobster tail, or they
may be shucked, or removed from the shell, with a special knife. Shucked
shrimp, scallops, oysters, and clams are often breaded and frozen.
Shrimp may also be sold with the intestinal tract removed, a form known
as "peeled and deveined."
Shucking bivalves such as clams and oysters is a somewhat dangerous
process. The hand holding the bivalve should be protected with a towel
or a metal-mesh glove. The hinge is severed as the shells are pried
apart, and the empty half of the shell is discarded, while the muscle
attachment to the other shell is spliced so the meat can be removed. An
average worker can shuck almost 7 pounds in an hour, but automated
shucking speeds up the process.
Oysters can be bought live in the shell, or shucked and then chilled,
frozen, or canned. Live oysters should have tightly closed shells. Any
gap between the shells means the oyster is dead and should be discarded.
Select shucked oysters which are plump and full-bodied; about one cup is
equal to one serving. If the oysters are in their shell, buy half a
dozen per person. Three varieties of oyster are commonly available in
the United States: Eastern oysters from the Atlantic coast, and Olympia
(small) and Japanese (large) oysters from the Pacific coast. Oysters in
the shell and well refrigerated have a longer shelf life than other
mollusks because their shells remain very tightly closed, while other
shellfish have a tendency to gape, making them more susceptible to
drying out and dying.
Clams can be bought in the same forms as oysters, and, as with oysters,
their shells should be closed tightly and there should be no decaying
odor. About six to eight shelled clams are required per serving. Two
major east coast types are hard-shell and soft-shell clams, with the
meat of hard-shell clams being less tender. Hard-shell clams include
cherrystones, which are the most common variety; littlenecks, which are
the smallest and most tender; and chowders or quahogs, which are the
largest. Soft-shell clams are also known as longnecks or steamers
because of the long tube extending from the shell opening. Since
soft-shell clams do not completely close, and are very susceptible to
drying out and dying. A limp neck hanging out of the shell signals that
the clam is dead and should be discarded. West coast varieties include
razor and Pismo clams.
In North America, the only part of the scallop that is eaten is the
creamy white or tan-colored abductor muscle responsible for opening and
closing the shell to move it through the water. Scallops cannot close
their shell tightly when taken from the water, so they are usually
shucked and then sold fresh, frozen, or canned. This sweet-tasting
mollusk varies in diameter from 1/2 to 2 inches, and about 1/4 to 1/3
pound is an adequate portion for one person. The three main varieties of
scallops available are bay scallops, which are small, sweet, and
delicate; sea scallops, which are larger and not as delicate; and calico
scallops, the least expensive and tiniest of all and the blandest in
flavor. Calico scallops are often sold cooked or frozen.
The black or dark-blue colored shells of common mussels should be
scrubbed free of barnacles, but the "beards" or black threads used to
attach the shells to solid foundations in the ocean should not be pulled
out until the mussels are ready to be cooked, because removing them
kills the mussel. Mussels are heated in their shells after being
purchased live, or they are shucked and packed in brine. Extremely
hollow or heavy-feeling mussels should be discarded, because they are
either dead or filled with sand. Also available are the larger,
green-lipped New Zealand mussels whose size makes them ideal for
stuffing and baking.