Oysters are a type of shellfish that is often eaten raw. As with all raw foods, oysters may be contaminated with harmful bacteria. Oysters, moreover, pose a relatively high health risk, in addition to a risk of hepatitis. This is because oysters filter large volumes of water to get their food, and therefore there's a good chance that any bacteria and viruses that may be in the water will build up in the oysters.

Oysters are quite nutritious – they contain minerals such as calcium and iron, and vitamins – and they're low in cholesterol too. Although today oysters are considered a luxury, in the past they were eaten by the dozen in poor communities.

If you're worried, you could cook your oysters – they will still taste delicious.

If you want to eat oysters safely, follow these tips:

Choosing – Fresh oysters should have tightly closed shells (this is actually the case for all shellfish). Don't choose any oysters if the shell is open and it doesn't close when you tap it.

Chilling – Oysters can be kept in the fridge for up to one week. Always throw away any oysters if their shells aren't tightly closed because this means they're already dead or dying. One side of the shell is ‘cupped'; put this side down and keep the flatter side up. Put them on a plate and cover with a clean damp cloth – never keep them in water. When you're ready to use them, first rinse them in cold water.

Freezing – You can keep oysters in a freezer for up to 3 months. Because freezing kills them, once you've thawed them they will be easier to open than fresh ones. Before freezing, wash them well, scrub the hinge end and throw away any that aren't tightly closed, then freeze. Eat them as soon as possible after you've thawed and cooked them.

Cooking – If you choose to cook your oysters there are several ways to cook them but one of the simplest is grilling. Heat the grill for ten minutes. Check that the oysters are still tightly closed, then carefully open and lay them in their half shells, open side up, on top of a piece of foil. Dot a little butter or olive oil on them and then grill for two minutes.