Scrubbed mussels and clams will purge themselves of grit or sand if left for an hour or so in cold salted water with a sprinkling of oatmeal or flour.
To open oysters, clams and scallops, use a strong thin knife with a blunt rounded tip, preferably an oyster knife. Oyster knives can be bought from good fishmongers or kitchen supply shops. Hold the shell in a cloth in the palm of one hand and force the blade between the two parts. Run the blade around the inner edge of the shell to sever both muscles, then twist the knife to prise open the oyster.
Mussels will open quite easily when cooked in the steam from their own juices, or with a little liquid or white wine. Place mussels in a saucepan, add a glass of white wine, cover the pan and place over a high heat for 4-5 minutes. Shake the pan frequently. When removing the cooked mussels, discard any that do not open.
