Getting to Know: Shellfish
Despite its name, shellfish are not fish (and they don't all have shells, either). They come in two basic models: mollusks, such as clams, oysters, snails, scallops, and mussels; and crustaceans, such as lobster, shrimp, crayfish and crab. Both can confuse shoppers; both are easy to overcook. Here are some tips from the test kitchen.
Clams are sold as hard-shell or soft-shell. Because hard-shell clams stay shut, they are less sandy and better suited to serving raw (smaller cherrystones and littlenecks) or baked and stuffed (larger quahogs). By contrast, soft-shell clams (steamers and razor clams) gape when they are alive, so they contain a lot of sand. If you're making clam broth, strain the sand out through a paper coffee filter.
The quality of lobster meat depends to a large extent on where the crustacean is in its molting cycle, during which the old, hard shell is replaced with a soft, new one. Hard-shell lobsters taste better and are meatier. To determine the stage of your lobster, just squeeze. A soft-shell lobster will yield to pressure. Like the roe? Look for a female. Her soft "swimmerets" (appendages under the lowest legs) give her away.
Crayfish—also known as crawfish, crawdads, or (our favorite) mudbugs—are closely related to lobsters. They live in fresh water, though. North America, particularly Kentucky and Louisiana, is home to more than half of the world's species. Soups, bisques, and étouffées use the tail portion of the crayfish, but at crawfish boils (great, messy fun in Louisiana and Texas), people eat the whole body (including the head) with gusto.
Whether you've got North Atlantic blue (found mostly on the East Coast) or "Mediterranean" mussels, scrub them with a stiff brush to remove any grit and debeard them (pull on the strands extending from the shell) before cooking. You can refigerate mussels for one day in a colander covered with a damp kitchen towel. If the mussels won't close when tapped, discard them.
The Dungeness is a Pacific crab with a range from Alaska to Baja, California. Only adult males at least 6 ¼ inches long can be legally harvested, so Dungeness crabs typically weigh at least 2 pounds. Their rich, firm meat is often compared to lobster meat. Boil live Dungeness crabs in water or in seasoned crab boil. If you don't live on the West Coast and can't get live crabs, buy cooked, frozen whole crabs. Defrost, crack, dress with vinaigrette, and toss with salad greens.
Such classic American dishes as crab imperial and crab Louis are best with blue crab (or its close cousin, the blue swimmer crab from the Pacific Rim). The Chesapeake Bay is famous for its blue crabs, although demand now outstrips supply. In that region, the crabs are typically steamed with vinegar and Old Bay seasoning, then cracked with mallets and slurped with melted butter. Soft-shell crabs are blues that have just shed their hard shell and not yet grown a new one.
Shrimp are sorted by size. Look for the letter U (for “under”) followed by a number. One pound contains fewer shrimp than that number, so the smaller the number, the bigger the shrimp. Once you get them home, the question is, to devein or not to devein? We tasted cooked shrimp both ways and didn’t find much difference. But let’s be honest: The vein is unattractive. To remove it and peel the shrimp in one easy step, snip along the crustacean’s back with scissors. Save the shells to make a quick, flavorful stock.
East or West? Each coast has die-hard fans. As a rule, Atlantic oysters are “crisp,” our tasters said, and briny with an intense hit of fresh, cold sea salt. (All Atlantic oysters are the same species: Crassostrea virginica.) They range from 2 inches long to nearly 6 inches long (Gulf Coasters call these "tennis shoes" for their size). Pacific oysters are rarely as salty and often taste complex and “fruity, like watermelon.”
Bay scallops, harvested from North Carolina to Maine, are small, cork-shaped scallops (they’re also sold as Nantucket scallops). Since their season is limited—fall through mid-winter—they’re pricey. One pound may include as many as 90 scallops. Chefs prize them for their sweet taste and use them in soups, stews, and stir-fries.
Surprise! Not all shellfish live in the ocean. The snail is a mollusk, therefore a shellfish, but many of those that we eat live on land. For instance, escargot—land snails served in a garlicky butter sauce—is one of the most famous dishes in French cuisine. But while we Americans happily dine on other mollusks, many of us are squeamish when faced with snails. In this country, intrepid eaters will likely find only frozen or canned (already cooked) snails; they merely need reheating.
Fishing for king crab, mostly done in Alaska, is seriously scary business. The peak season is winter, when all too often fishermen die of exposure (or drowning). Among the three species of king (red, blue, and golden), red is best, and the leg meat is prized above all else. The legs are meaty, sweet, mild, and big—10 to 12 inches long. Most king crab is sold cooked and frozen. To reheat the legs, we like to steam them, which preserves their firm texture.
Unlike bay scallops, the larger sea scallops are in markets year-round. They’re shucked at sea, so before cooking, simply remove the crescent-shaped muscle that attaches the scallop to the shell. Avoid “wet” scallops (ask at the store), which are treated with a solution of water and sodium tripolyphosphate to preserve them. But if wet is all you can find, soak them in 1 quart of cold water, ¼ cup of lemon juice, and 2 tablespoons of salt for 30 minutes to mask any chemical flavors.