When we think about the world of shellfish, there is tremendous diversity to consider—and there always seem to be new things to discover. Just last week I tried a new variety of clam that I hadn't eaten before. Here, I'll focus on some of the better-known and widely available mollusks that we know and love.
Shellfish is a broad culinary term that can be broken down into mollusks, crustaceans, and echinoderms. Mollusks include bivalves (clams, mussels, oysters, and scallops, etc.), gastropods (abalone, whelks and other sea/freshwater/land snails, limpets, etc.), and cephalopods (squid, octopus, cuttlefish, etc.). Crustaceans include crabs, shrimp, and lobsters. Lastly, echinoderms include sea urchins and sea cucumbers. Here's what a cook should know about the popular bivalves clams, mussels, and scallops.
When selecting shellfish, it's generally a good rule of thumb to look for shells that are tightly closed. Like most truisms, this one has exceptions, and mussels are one. Some shellfish tend to gape, and this is not a sign that they are dead—often it is a sign they are thirsty. Mussels like to be well hydrated and they will gape a bit when they start to lose moisture. If you are going to store mussels in your fridge at home for more than a day, it's best store them so they keep hydrated. I like to nestle a colander over a bowl, place the mussels in the colander, and cover them well with ice. The bowl will catch the water from the melting ice and keep your fridge neat. You can store mussels like this for several days before using them in your favorite mussel recipe.
Most of the mussels for sale are farmed. These are usually very clean and require little more than a good rinse before cooking. If you do find wild mussels (which can be very delicious) they will need to be debearded before you cook them. To do this, you'll pull out the fuzzy "beard" that protrudes from the middle of the mussel. Once this is done, give them a rinse as you would their farmed counterparts. While you shouldn't discount/discard an uncooked gaping mussel, it is best to discard any shellfish that don't open when you cook them.
There are two types of clams we commonly eat, soft-shell clams and hard-shell clams. On the East Coast the most well-known type of soft-shelled clams are steamer clams. "Steamers," as they are affectionately known, are a real summertime treat (though they are available year round). They are also the clams you're eating when you order whole belly fried clams. Razor clams are another variety of soft-shelled clam and they are found on both coasts. Pacific razor are larger and wider than their East Coast cousins. Both are great raw, steamed, or seared.
Fishermen dig steamer and razor clams by hand when the tides are low. Like mussels, steamer and razor clams both naturally gape open. Both of these clam varieties can be sandy. Many steamers are already purged to remove the sand when you buy them; ask your fishmonger if this is the case. If not, steamers and razor clams should be purged at home. There are a lot of old wives tales regarding the purging of shellfish. Let's dispel some of that bad information here: Do not add flour or cornmeal to your purging water, the shellfish being purged will not eat these things. Do not salt the water, as you cannot recreate a marine environment this way. There is no way around the fact that purging shellfish is hastening their demise, so it is important to purge your shellfish as close to your planned cook time as possible. To do this, place your shellfish in a bowl with lots of room for clean, fresh, cold water. Give the shells a good toss in the water and place the bowl in the fridge. You'll want to purge for 20-30 minutes, no more. If you can give the shells another toss or two during this time, the agitation will encourage the animals to spit out the sand in their bellies. Once the purge time is done, lift the shellfish from the bowl; the sand they spit out is resting at the bottom, so leave that be. Your clams are now ready to cook and eat.
The most common hard-shelled clams on the East Coast are Northern Quahogs. These are sorted by size. Count necks are the smallest; followed by little necks, top necks, cherrystones and quahogs (the biggest of the bunch.) The smaller sizes are ideal for eating raw, steaming and tossing with pasta. Larger clams are preferable for stuffing or using in chowders. Manila clams are very small hard-shelled clams from the West Coast. They are sweeter and less briny than quahogs, and are delicious in any steamed preparation, in soups and with pasta.
You can keep fresh clams for up to a week at home. Place them in a bowl in your fridge and cover them with a damp cloth to protect them from the blowing of your fridge's fan. When you’re ready to cook your clams give them a good rinse, paying special attention to their hinges—this is where grit will accumulate. Do not purge hard-shelled clams! It is unnecessary and can compromise their quality.
There are two primary varieties of scallops that are fished domestically, mostly in New England and the Mid-Atlantic. You will usually find them shucked, though they are sometimes sold live in their shells. Sea scallops are larger and are fished for year round. Tiny bay scallops are a seasonal delicacy that I look forward to every year. They are super sweet and burst with natural sugars. Their season starts around the beginning of November and goes until late winter/early spring. They are not to be confused with imported farmed bay or calico scallops, which are of a lower quality.
Scallops are frequently treated with sodium tripolyphosphate, which causes them to take on water weight. Treated "wet" scallops will be limp and release a milky liquid. Avoid them; they will never cook properly and can have an off flavor. Look for "dry" untreated scallops. They should smell sweet and fresh, and feel firm and a little tacky to the touch. Both sea and bay scallops are great served raw or cooked in your favorite recipes. Store them in a sealed container in the coldest part of your fridge. Scallops are best eaten within three days of purchase—they tend to lose their sweetness with age.
Watch how to shuck a hard-shell clam: