An oyster knife is a knife which has been specially designed for the purpose of opening oysters. It is an absolute must have if you want to prepare oysters, and it helps with other shellfish as well. Most kitchen supply stores sell oyster knives, and they are often available from fishmongers as well. They are generally inexpensive and very easy to care for, making them a worthy addition to one's kitchen supplies.
The shape of the blade on an oyster knife varies, although the blade is often triangular. It is also blunt, reducing the risk of injury, short, and very thick. A well-made oyster knife will have a thick, comfortable handle which is made from a non-slip material such as textured silicone. This ensures that cooks can hold and use the knife comfortably to shuck oysters, without worrying about hurting themselves.
The process of opening an oyster can be difficult, because most oysters reflexively clamp shut when they sense that something wants to eat them. This is an understandable response which is shared by all shellfish, and unfortunately for cooks, shellfish should only be used when it is alive at the time of cooking, to reduce the risk of foodborne illness. As a result, it is often necessary to wedge shellfish open, unless they are being prepared whole.
To use an oyster knife, the blade is wedged into the shell very close to the hinge at the narrow end of the shell. It may take some pressure to get inside, and once the blade has penetrated, it is twisted to encourage the shell to crack open. After the shell has been levered open, the top shell can be removed, and the oyster knife can be used to cut through the strip of muscle which keeps the shell attached. Then, the oyster is ready for consumption or cooking.
Most people recommend that you scrub oysters before opening them, to avoid transferring potential bacteria into the oyster when you open it. It helps to do this under running water, and then to refrigerate the oysters on a tray for an hour or so to promote relaxation of the muscles which hold the shell shut. It is also a very good idea to hold an oyster in a towel when you shuck it, rather than in your bare hands. This will protect you from the sharp edges of the shell, along with shards of shell which may crack off when the shell is opened. It will also protect your hand if the blade slips while you shuck.