The crab legs most commonly found in grocery stores all across America are typically one or more species of the snow crab (Chionoecetes sp.). The two most common species are bairdi and opilio crabs. The bairdi crab, sometimes known as tanner crab, is the bigger of the two at 2 pounds, growing up to twice the size of an opilio crab. Either one will be quite delicious, so don't fret about which one you should get. Unless, of course, you actually have a preference.
Providing that you buy American caught crab, you can be fairly certain that the crab you are eating is not the last of its species. Basically what I'm saying is that you shouldn't buy imported crab, as the crab fishing policies of other countries may not be as stringent. That is, unless you want this season of Deadliest Catch to be its last. If you don't know what I'm talking about, you are missing out on one of the only reality TV shows worth watching.
1. Pick up some crab legs. When crab is in season, it is readily available at almost any grocery store. And even for a few months after, if it's frozen. Basically this means that it's available all year long. After being caught, crab is kept alive until the boat carrying it reaches port. Once there, the entire catch is quickly cooked, processed, frozen, and packed.
2. Break up the crab clusters. My steamer isn't big enough to cook the crab clusters whole. Unless you have an extra large, Chinese steamer on hand, I'm guessing they won't fit in your steamer, either. Breaking off the body is the best way to make the clusters fit. You may also have to bend the crab legs a little to get them to fit.
3. Put the crab into the steamer. Since the bodies are bigger and may require more cooking, I put them in the bottom of the pot where the steam should be hotter. Ideally, this should cook them quicker. Fill the bottom of the steamer pot with 3–4 inches of cool water. Heat the pot until you get a rapid boil.
4. Cover the pot and steam the crab legs. Once the pot is boiling, put the steamer basket into the pot and replace the lid. Monitor the pot for the next few minutes until steam begins to develop. Thawed crab legs should steam for 5–6 minutes, and frozen legs will take about 10–12 minutes. Check the inside of a claw with a thermometer. It's done when the crab leg reaches 155 degrees.
Buy crab caught by American crab boats; no imported crab!
Cook thawed crab the same day.
If you somehow get live crab, cook it while it's still alive. You don't want to cook a raw, dead crab. It's the reason the professionals cook their live crab right when they get to port.
Don't forget about the body meat. It is quite delicious! You may need to cut the body in half horizontally to get the meat out easier. Or use a small fork.
The crab is already cooked, so all you need to do is get it back up to a safe temperature. You can do that anyway you want. Wet heat (boiling and steaming) works best, but some form of grilling might work okay, too.
Leftover crab should last a few days, but it may be best to just make some crab cakes with it the next day.