There are few pleasures to match a bowl of mussels eaten within sight of the water they came from. Sweet, salty, cheap and quick to cook, they are the shellfish that rewards a little care and very little skill. If you live near the coast, or you are travelling it for a week with a self-catering kitchen, mussels are the easiest possible route to a proper seaside supper. And because the best of them come from rope-grown beds along our own shores, you can eat them with a clear conscience.

Why Mussels Suit Coastal Cooks So Well

Mussels are the most sustainable shellfish we have. Rope-grown mussels — the sort suspended from long lines in sheltered sea lochs, estuaries and straits — feed by filtering plankton from the water, need no feed, no antibiotics and no fresh water, and actually improve water quality as they grow. Harvesting them is gentle on the seabed, and the crop is ready in eighteen months to two years. Wild mussel beds are gathered too, under strict licensing, but the rope-grown ones are usually plumper, cleaner and grit-free.

They are also cheap. A kilo, which feeds two people generously with bread and a salad, costs less than a single portion of most white fish. That is a rare thing in coastal cooking, and it is worth taking advantage of.

Sourcing: Buying from the Beds

If you can buy direct from a harbour stall, a fisherman's co-operative or a quayside shed, do. Ask when they were landed — the answer should be "today" or "yesterday". Fresh mussels smell of the sea and nothing else; if there is an ammonia note, walk away.

• Closed shells: a live mussel holds its shell tightly shut. Open ones should close when tapped sharply on a hard surface.
• Weight: they should feel heavy for their size, full of seawater and meat, not hollow and light.
• Condition: unbroken, no mud-filled cracks, no shells that gape and stay gaping.
• Classification: legitimate UK beds are monitored and classified for water quality. Buying from a registered supplier means the shellfish have been through that testing.

Take a cool box or a chiller bag to the harbour. Mussels die quickly in a warm car boot, and dead mussels are the ones you will be throwing away an hour later.

Preparing Mussels Properly

Get home, or back to the cottage, and deal with them straight away. Tip them into a large bowl or the sink and run them under cold water, turning them over with your hands. Scrub each shell with a stiff brush or the back of a knife, scraping off barnacles, grit and any thread of weed.

• Debeard: pull the wiry "beard" away with a firm tug towards the hinge. It should come easily once the mussel is alive and fresh.
• Discard any that stay open after a sharp tap, and any with cracked or broken shells. Be ruthless — one bad mussel can spoil a whole pan.
• Do not soak in fresh water. It kills them. If you must hold them for a few hours, keep them in a colander over a bowl in the coldest part of the fridge, covered with a damp cloth.
• Cook them the same day where possible. They will keep overnight chilled, but no longer.

A Cider, Garlic and Parsley Steam

This is the supper I cook most often when the tide has been kind. It takes ten minutes and needs nothing but bread.

• 2 kg live mussels, prepared as above
• 2 shallots or 1 small onion, finely chopped
• 3 garlic cloves, sliced thin
• 40 g butter
• 300 ml dry cider — a West Country or Norman one works beautifully
• A large handful of flat-leaf parsley, chopped
• Black pepper, and plenty of crusty bread

Use your largest pan, one with a tight-fitting lid. Melt the butter over a medium heat, soften the shallots and garlic for three or four minutes without colouring them, then pour in the cider and let it bubble for a minute. Tip in the mussels all at once, clamp on the lid and steam for four to six minutes, shaking the pan once or twice.

They are done the moment the shells have opened. Lift the lid, scatter over the parsley and a good grind of pepper, and turn them through the liquor. Discard any that remain shut after cooking — that means they were dead before they went in. Serve in deep bowls with the broth spooned over, and bread to mop up every drop. Some people add a spoonful of cream at the end; I would not, but I understand the impulse.

Eating Along the Coast

Part of the joy of mussels is the geography. A day spent walking a harbour wall, checking the tide tables and watching the light come off the water makes the eventual bowl taste better. If you are travelling, plan your supper around the boats: buy in the late afternoon from the harbour, cook early, eat while the gulls are still arguing. Coastal paths, ferry crossings and cold evenings all point towards the same pan.

Safety, Storage and Good Habits

Never gather mussels from a beach you do not know, whatever the locals say. Some stretches are closed because of algal blooms, sewage discharges or industrial pollutants, and the risks change with the season and the weather. Trusted beds are monitored for exactly this reason. When you buy, keep the shellfish cold, cook them through and eat them promptly; do not reheat leftovers. If you have collected your own from an authorised area, check with the local authority first, and leave the small ones behind so the beds recover.

Get the basics right — rinse thoroughly, be strict about open shells, keep everything cold — and you have a coastal supper that costs very little, tastes of the place you are standing in, and leaves the water cleaner than it found it. That is a good way to eat by the sea.