How do I defrost fish properly?

Fish is the least forgiving thing in the freezer, because it spoils faster than meat once thawed and because most of it is vacuum-packed, which introduces a hazard nothing else in the freezer has. The whole job is: get it out of the pack, keep it cold, and let the drip go somewhere other than back into the fish.

Safety

What you'll need

• A rack and a plate or tray
• A sealable bag if using the cold water method (optional)

Step by step

1. Open the vacuum pack before thawing, not after.Cut a corner off or slide the fillet out entirely. This is the one instruction on the pack that people skip, and it is there because an anaerobic pack plus a rising temperature is the specific condition that lets botulinum toxin form.
2. Thaw in the fridge, on a rack, overnight.A rack over a plate keeps the fillet out of its own drip. Most portions are ready in eight to twelve hours; a whole side of salmon or a thick loin takes closer to twenty-four.
3. Use cold water if you need it faster.Seal it in a bag with the air pressed out, submerge in cold water, and change the water every twenty minutes so it does not warm. A fillet takes around an hour. Never use warm or hot water — the outside enters the danger zone long before the middle thaws.
4. Stop while it is still slightly icy in the middle.Fish that is fully soft has usually gone slightly too far and will be softer in texture. Slightly firm in the centre is the target, and it will finish in the twenty minutes before it hits the pan.
5. Drain it and dry it hard.Pour off everything on the plate. Press the fillet between kitchen paper on both sides until it is genuinely dry. Thawed fish holds more surface water than fresh, and that water is what stops it browning.
6. Cook it the same day.Thawed fish has a shorter life than fresh, not the same one. Treat it as needing to be cooked within twenty-four hours, and sooner if it was thawed in water.
7. Do not refreeze it raw.Each freeze-thaw cycle ruptures more cells and the fish gets progressively mushier and more prone to spoilage. If you have thawed more than you need, cook it all and freeze the cooked dish instead.

Tips

• Frozen prawns thaw in a colander under a gentle cold tap in about five minutes and are the one case where speed costs nothing.
• Thin fillets — plaice, sole, small fillets of bass — are usually better cooked from frozen than thawed, because thawing damages them more than the cooking does.
• If you forgot entirely, cooking from frozen is a legitimate answer for most white fish and salmon. It is not a compromise, just a longer, gentler cook.
• Label fish going into the freezer with the date and the species. Frozen white fillets are indistinguishable from each other after a month.

Common mistakes

• Thawing fish in the sealed vacuum pack — It is printed on the pack as a warning for a real reason: a sealed anaerobic environment warming up is the precise condition for botulinum toxin production, and the toxin is not destroyed by normal cooking.
• Thawing on the worktop — The surface of the fillet sits at room temperature for hours while the centre is still frozen. Fish spoils faster than almost anything else and the outside is where the bacteria are.
• Thawing in hot water to speed it up — It part-cooks the outside into an opaque rim while the middle is still solid, and it puts the fish into the danger zone for a long time. Cold water changed regularly is nearly as fast and entirely safe.

Questions people ask