Wash them thoroughly – grit will destroy your meal
When you buy your mussels – either from a fishmonger or from the supermarket – look for mussels that are tightly closed. That’s a good sign of freshness. When you’ve got them home, put them in the fridge to keep cool and, ideally, cook them the same day you bought them.
Before you cook them, you need to clean them. Rope-grown mussels are usually very clean, but mussels that have been dredged from the seabed will have barnacles on them and grit inside. Place the mussels in the sink under running water. Pick up each mussel and check that it’s firmly closed. Discard any mussels that are open – that’s very important. Scrub each mussel clean with a stiff brush to get rid of any barnacles, pulling off the hairy ‘beard’ that sticks out from the shell, if it has one.
You don’t want any grit in your rich sauce. Keep the cleaned mussels under the running water. It’s really important that the water stays moving over the mussels, but that they’re not soaking in it. If you leave them soaking in tap water, they’ll die and that’s not what you want.
For a classic dish, try my Mussels with White Wine (moules marinière).