Can I reheat steamed milk?

You can heat it. You cannot restore it.

What happens the first time

Steaming does two things at once: it heats the milk, and it forces air into it which proteins then stabilise into foam. Both changes are structural. The proteins denature — they unfold and rearrange to hold the bubbles — and that is a one-way process.

What happens the second time

Re-steaming already-steamed milk gives thin, coarse, unstable foam, because the proteins have already done their job and cannot do it again. And because the milk is being taken through the heat range twice, the lactose degrades further and the flavour turns distinctly cooked, sometimes eggy.

You end up with hot milk that tastes worse and behaves worse.

The practical advice

Texture only what you need. That means measuring: a flat white takes about 130 ml of milk, a latte about 200, a cappuccino about 150. Pour it from a jug filled between a third and a half.

If you routinely have milk left over, buy a smaller jug. It is a cheaper fix than wasting milk, and small jugs texture better for single drinks anyway.

What to do with leftovers

Drink it, cook with it, or put it in the fridge for a non-coffee use. What you should not do is save it for the next coffee.

The exception nobody mentions

Very slightly warmed milk that never reached foaming temperature — under about 37 °C — has not undergone the structural change, and it will still steam properly. That is the only case where reheating works.