Why does my milk catch and burn?

What is actually sticking to the bottom of the pan, and the four things that stop it happening.

Difficulty: beginner
Time: 10 min
Read: 3 min
Safety: caution

Short answer

Milk proteins settle and stick to a hot pan base, then scorch. Heat it gently, stir with something flat that reaches the corners, use a heavy pan, and rinse the pan with cold water first so the proteins have less to grip.

Burnt milk taints a whole pan of sauce, hot chocolate or porridge with a flavour nothing removes. The mechanism is simple and so are the fixes, but they have to be applied before it happens rather than after.

Safety

Milk boils over suddenly and the foam that comes up the sides is scalding. Never leave a pan of heating milk unattended, and take care lifting a pan that has just boiled over — the outside and the hob will be wet and slippery.

Step by step

Understand what is catching.Milk proteins denature with heat, sink and adhere to the hot metal. Once a layer is stuck, it insulates and overheats, and the scorched flavour goes through the whole pan.
Rinse the pan with cold water before you start.Pour in a little cold water, swirl and tip it out without drying. The thin film of water left behind gives the proteins something to sit on rather than bare metal. It genuinely helps.
Use a heavy-based pan.A thin pan has hot spots directly over the burner where milk catches first. A thick base spreads the heat and is the single biggest equipment factor.
Heat it gently.Medium-low, and give it time. Milk on high heat catches before it is warm through, and it will not heat faster in any useful sense — it just burns at the bottom.
Stir with something flat that reaches the edges.A flat wooden spatula or a silicone one, not a spoon. The join between base and side is where a spoon never reaches and where the burning starts.
Keep it moving and watch it.Milk goes from steaming to over the sides in seconds because the skin traps the steam until it lifts. It needs actual attention, not occasional glances.
Take it off before it boils.For most purposes milk should be scalded — steaming, small bubbles at the edge — not boiled. Boiling adds nothing and makes catching much more likely.
Deal with a pan that has caught.Do not scrape and carry on: the burnt flavour is already in the milk. Pour the good milk into another pan if you catch it very early, otherwise start again. Soak the pan in cold water with a little bicarbonate.

Tips

A microwave in short bursts, stirring between, avoids the problem entirely for a mug's worth.
Semi-skimmed and skimmed catch more readily than whole milk, because fat provides some protection.
Anything sugary added to milk — chocolate, sweetened cocoa — dramatically increases how easily it catches. Add it after the milk is hot.

If it doesn't work

A brown skin stuck to the pan base

Cause: Milk proteins settling on metal that is too hot — Fix: Lower the heat, use a heavier pan, and rinse the pan with cold water before adding milk next time.

Milk boils over without warning

Cause: The skin on top traps steam until it lifts suddenly — Fix: Heat gently, stir to break the skin, and take it off at steaming rather than letting it boil.

Questions people ask

How do I stop milk sticking to the pan?

Rinse the pan with cold water and do not dry it, use a heavy-based pan, heat gently, and stir with a flat spatula that reaches the corner between the base and the side.

Does milk need to boil?

Rarely. For most uses it should be scalded — steaming with small bubbles at the edge. Boiling adds nothing and makes it far more likely to catch or boil over.