What is the white stuff that comes out of chicken and bacon?

Two different white things get confused here. The white foam that seeps out of chicken breast and salmon is albumin. The white liquid that floods a pan of bacon is brine plus dissolved protein. They come from the same mechanism and they mean slightly different things.

Step by step

1. Know what albumin is.Albumin is a soluble protein found in muscle. In raw meat it is dissolved in the water held between the muscle fibres. When heat contracts those fibres, the liquid is squeezed to the surface, and as it goes it passes through the temperature at which albumin denatures and sets — the same thing that happens to egg white. What you see is protein coming out of solution.
2. Recognise that it is not fat, and not pus.Fat is translucent when melted and yellow-white when solid, and it pools rather than foams. Albumin is opaque, matt, and clings. The persistent internet claim that it is pus has no basis; it is one of the ordinary proteins that make up the meat you are eating.
3. Read it as a sign the heat was too high.Gentle cooking lets the fibres contract slowly and the liquid stays put or leaves gradually. Aggressive heat contracts them hard and fast and forces the liquid out in one go. If a chicken breast or a salmon fillet is producing a lot of white foam, turn the pan down.
4. Read it as a sign the meat was frozen.Ice crystals rupture cell walls. Meat that has been frozen and thawed holds its water less tightly, so more liquid — and more dissolved protein with it — leaves during cooking. Previously frozen chicken almost always foams more than fresh.
5. Read the bacon version differently.The white liquid flooding a pan of bacon is mostly brine from a wet cure, with dissolved protein in it. It boils rather than fries, the pan temperature drops and the bacon goes grey. Dry-cured bacon produces very little. This is the most reliable practical test of how much water you bought.
6. Reduce it if it bothers you.Brine or dry-brine the meat beforehand, which improves water retention. Cook at a lower temperature. Pat the surface dry before cooking. Buy dry-cured bacon and chicken without an added-water declaration. Sous vide produces almost none, because the temperature never spikes.

Tips

• Salmon shows it most dramatically because it is high in albumin and cooks fast. The same rules apply — lower heat, and a short brine before cooking noticeably reduces it.
• You can scrape it off with the edge of a spoon before serving. It has no flavour and there is nothing wrong with it, but it does not look appetising.
• The same protein makes the scum on the surface of a stock. Skimming it produces a clearer stock; leaving it makes no difference to safety.
• If a chicken breast in the fridge is sitting in a lot of liquid before you have cooked it at all, that is purge — a sign of added water or of a long time since packing, not a spoilage signal on its own.

Common mistakes

• Throwing meat away because of white residue — It is a normal cooking phenomenon and appears on perfectly fresh meat. Spoilage is judged by smell, sliminess and date, not by this.
• Turning the heat up to boil the liquid away — More heat squeezes out more liquid, so it makes the problem worse. Pour the liquid off and let the pan recover instead.
• Assuming it means the chicken was 'injected' — It happens with completely unadulterated meat too. Added water makes it worse, but heat and previous freezing produce it on their own.

Questions people ask