How to prepare and store fresh seafood at home

Prawns, mussels or squid don't land on our table every week, so each time I buy them it feels like a small treat. And each time the same thought follows me home: the bag is warm, the car is stuffy, and I'm not cooking until this evening or tomorrow. Seafood doesn't forgive carelessness. You can leave a bag of potatoes in the hall and get away with it; prawns and shellfish are another matter.

Storing it properly takes care of three things at once. First, safety: the NHS says plainly that fish and shellfish that aren't fresh, or haven't been stored and prepared hygienically, can cause food poisoning. Second, money: seafood isn't cheap, and throwing half a pack away stings. Third, flavour: a prawn that has spent a day in the right place stays firm and sweet rather than woolly.

Below is how I handle seafood from the shop to the pan. I lean on advice from the NHS and the Food Standards Agency (FSA); the rest is simply how we do things in our kitchen.

Straight home and straight into the cold

The first rule is simple, and the NHS puts it without any ifs: put fish and shellfish in the fridge or freezer as soon as you get home. So I pick up seafood last, once everything else is in the trolley, and I don't stop off anywhere on the way back. In summer I take a cool bag with a couple of ice packs.

The FSA advises keeping the fridge between 0 and 5°C and checking it with a thermometer about once a week. A basic fridge thermometer costs less than a bag of prawns, so ours lives in the fridge for good, and I glance at it whenever something perishable goes in.

Exactly where to keep it. The FSA recommends storing raw meat, poultry and fish in their packaging or in clean sealed containers on the bottom shelf of the fridge, so they can't touch or drip onto other food. Seafood goes there too, right at the bottom, in a deep bowl or tray.

> Natalia's tip: I always slide a plate or a lipped tray under a bag of prawns. Even when the packet looks intact, it can weep a little as it defrosts or just from condensation, and then the bottom shelf takes a minute to wipe rather than half an hour.

Live shellfish need air

Mussels, oysters and clams are a little different, because they are often sold alive. The NHS reminds us not to put live shellfish into airtight containers: they need to breathe. Everything else, by contrast, should sit in covered containers.

Another NHS rule that surprises people: don't store fish or shellfish in water. It seems natural to fill a bowl and keep mussels "as if in the sea", but that is exactly what you shouldn't do.

How I keep live mussels until the evening:

• I tip them out of the net into a wide bowl, in a single layer as far as possible;
• I cover them with a clean damp tea towel, but no lid;
• I put the bowl on the bottom shelf of the fridge;
• I cook them the same day.

The check before cooking. The NHS advises throwing away mussels, oysters, clams or any other live shellfish if the shell is cracked or broken, or if it is open and doesn't close when tapped. A live one will clam up at a gentle tap. I go through the mussels one by one over the sink: I tap any open ones on the edge of the bowl and wait a few seconds. If the shell still hasn't closed, it goes in the bin without a second thought.

Prawns, squid and fish: cover them and don't hang about

Raw prawns, squid or scallops from the chilled counter go into a clean lidded container if the original packaging is torn or awkward. I check the "use by" date on the label straight away, along with the storage instructions: the FSA advises following the storage instructions on the packaging.

If I can see I won't cook it in time, the freezer comes to the rescue. The FSA says you can freeze food right up until midnight on the "use by" date printed on the label. The freezer, by its guidance, should run at around -18°C.

It helps to understand what the cold actually does. The FSA explains that at -18°C bacteria aren't killed; they are put on pause and may revive as the food defrosts. So the freezer buys time, but it can't rescue something that has already sat about in the warm.

> Natalia's tip: I freeze prawns in small flat bags, one supper's worth each, and write what's inside and the date on every bag. A flat bag freezes faster and defrosts more evenly than one big lump.

How to defrost frozen seafood

The NHS advises thawing frozen fish or shellfish in the fridge overnight. The FSA explains why: in the fridge, food stays out of the so-called Danger Zone of 8 to 63°C, where bacteria may grow.

What I do in practice:

1. In the evening I move the bag from the freezer to a bowl on the bottom shelf of the fridge.
2. In the morning I check the middle has fully thawed. The FSA warns that partially defrosted food may not cook evenly, which means harmful bacteria could survive the cooking.
3. If I forgot the night before, I use the defrost setting on the microwave directly before cooking, which the FSA allows.
4. I cook defrosted seafood the same day. The FSA advises using food within 24 hours of it being fully defrosted, because it will go off just as fresh food would.

Hygiene in the kitchen

Seafood deserves the same care as raw chicken. The NHS gives a few simple rules, and I follow them every time:

• wash your hands thoroughly before and after handling fish or shellfish;
• keep raw fish and shellfish, and any liquid from live shellfish, away from cooked or ready-to-eat food;
• use separate boards, plates and utensils for raw seafood and everything else.

I keep a plastic chopping board just for fish and seafood and wash it in hot soapy water as soon as I've finished. I make the salad to go with the prawns first, before I open the bag.

Who should take extra care

This part is for anyone with a pregnant guest, a toddler or an older relative at the table. The NHS says that shellfish such as mussels, clams and oysters that are raw or not thoroughly cooked can contain harmful viruses and bacteria, and that thorough cooking usually kills them. It advises older people, pregnant women and anyone with a weakened immune system to avoid raw or lightly cooked shellfish, and the same goes for young children. Raw shellfish shouldn't be given to babies and children.

One more thing: the NHS notes that fish and shellfish allergies are fairly common and can cause severe reactions, and cooking doesn't make a reaction any milder. If you're inviting friends round for a prawn supper, it's worth asking beforehand.

Common mistakes

1. Leaving the bag somewhere warm "for half an hour". The NHS advises getting fish and shellfish into the cold as soon as you're home. Every extra hour in a warm car or on the worktop works against freshness.
2. Shutting live mussels in an airtight box or covering them with water. Live shellfish need air, and the NHS advises against storing fish or shellfish in water.
3. Defrosting prawns on the worktop. That puts them in the Danger Zone of 8 to 63°C. The FSA advises defrosting in the fridge, or, if you're short of time, in the microwave on the defrost setting just before cooking.

Where it comes in: SweetEat recipes and notes

• Fresh fish without a market stall — how I choose fish in an ordinary shop.
• After fish I rinse the fish slice and dry it — a small habit for a clean kitchen.
• Light summer prawn salad — somewhere to use a bag of prawns.
• Seafood cocktail salad — the party version.
• Three good fish suppers — for a fish night.

Frequently asked questions

How should I keep live mussels before cooking?

The NHS advises against putting live shellfish in an airtight container, because they need to breathe, and against storing them in water. Keep them in the fridge in an open bowl under a damp tea towel and cook them as soon as you can.

How do I know a mussel should be thrown away?

The NHS advises discarding shellfish if the shell is cracked or broken, or if it is open and doesn't close when tapped. A live mussel will clam up at a gentle tap.

How do I defrost prawns safely?

The NHS advises thawing frozen fish or shellfish in the fridge overnight. If you're short of time, the FSA allows the microwave defrost setting directly before cooking. Use defrosted prawns within 24 hours.