If you are cooking or using oysters in a recipe, and don't want to shuck them open, steam them just until they open and scrape them out of the shell. When cooked their shells pop open; discard those that do not open after cooking. Oysters still in the shell are best eaten soon after they arrive.

What happens if oysters don't open after cooking?

If the shell remains shut after cooking, he says, “the muscle that holds the shell together is working. It's alive. Or if an oyster, clam or mussel doesn't open when it's cooked, sometimes it's dead — killed in the cooking process — but the muscle is just so joined to the shell that it's not letting go.”

Are oysters bad if they are open?

An open bill that will not close to the touch usually indicates the oyster is dead. All oysters should be alive right before consumption, and eating a dead one can be dangerous (see #4). Even if it smells and looks fine, but was open, I'd say best to avoid.