What is freezer burn and is the food still safe?

Those pale grey patches and the frost inside the bag look like the food has gone off, and they cause a lot of perfectly good meat to be thrown away. What has actually happened is that the food has dried out from the outside in, slowly, at minus eighteen degrees.

Step by step

1. Recognise what it looks like.Greyish-brown or greyish-white patches, dry and leathery or icy and opaque, usually on the surfaces that faced an air pocket. Frost or ice crystals stuck to the inside of the bag. Meat and fish show it most obviously; bread goes dry and crumbly rather than discoloured.
2. Understand the mechanism.Ice on the surface of the food sublimes — it turns directly to vapour without melting — and that vapour moves to the coldest surface nearby, which is the packaging, and refreezes there as frost. Every time the freezer's compressor cycles or the door opens, the small temperature swing repeats the process.
3. Treat it as quality, not safety.Freezer-burnt food is safe. Nothing has grown on it, because nothing grows at −18°C. The affected part is dry, tough and flat-tasting and the rest is fine. Cut the patches off and use the rest.
4. Pack food so no air touches it.Wrap tightly with the material pressed against the surface. Press the air out of freezer bags — flatten the bag round the food and seal the last corner as you push the air out, or use the water displacement trick of lowering a sealed-but-for-a-corner bag into water so the pressure squeezes the air out.
5. Double-wrap anything staying more than a month.Cling film or foil directly on the food, then a freezer bag or an airtight box. The inner layer excludes air from the surface; the outer one protects against knocks and door-opening temperature swings.
6. Freeze liquids flat and stack them like books.Bags laid flat freeze fast, have almost no trapped air, take up little space and thaw quickly. It is the best format for stews, soups, sauces and mince.
7. Label everything with contents and date.Most freezer burn is really a time problem — a bag that was fine at three months and forgotten for two years. A label and a list on the door are what stop that.
8. Keep the freezer at −18°C and reasonably full.A warmer freezer, or one that swings in temperature because it is nearly empty or the door is opened constantly, produces freezer burn much faster. A full freezer holds its temperature better.

Tips

• Open-freeze loose items — berries, chips, meatballs — on a tray first, then bag them tightly. You get separate pieces without air packed round each one.
• Vacuum sealing is the most effective prevention there is for freezer storage, since it removes the air entirely. Note that a vacuum-sealed low-acid food is a freezer or fridge item, never a cupboard one.
• Ice cream with a crust of ice crystals is the same phenomenon. Press cling film onto the surface before putting the lid back on.
• Badly freezer-burnt meat still makes good stock. The dryness matters much less once it has simmered for three hours.

Common mistakes

• Throwing away freezer-burnt food as unsafe — It is a texture and flavour fault only. Nothing has grown and nothing has spoiled. Trim the dry patches and use the rest, or use the whole thing in a stew or a stock where it matters far less.
• Freezing in the shop's packaging for months — Supermarket meat trays and loose film are designed for a few days in a chiller, not months in a freezer — they trap air against the meat. Rewrap anything going in for more than a couple of weeks.

Questions people ask