Bivalve molluscs that grow, wild or farmed, on coastlines around the world. Of particular interest are: the European oyster (known as a ‘native’ in Britain), which has a round flat shell; the Portuguese, an oyster with a concave whitish–brown shell, now thought to be the same as the Pacific oyster; the greyish shelled American oyster; and the Sydney rock oyster. Oysters are often named for their place of origin—Breton, Colchester and Sydney. The old rule of eating them only when there is an ‘r’ in the month applies only to the European oyster in Northern Europe. These spawn inside the shell, which makes the flesh, full of baby shells, very gritty. Oyster farming is a highly skilled occupation and today, when most oysters are cultivated, oyster lovers rely heavily on the oyster farmer for both flavour and safety. Ideally, an oyster should be bought live, with the shell closed. In this state, it should be heavy and full of water. If buying an open oyster, prick the cilla (little hairs around the edge of the flesh): it should retract if the oyster is alive. Look for plump, glossy oysters that smell fresh. Unopened, oysters can be kept in the fridge for up to 1 week. If opened, store in their liquid and eat within 24 hours.