Irrelevant question of the day

[WhatsitallaboutAlfie1]

What I want to know is this...why doesn't the milk used in lattes bought at Starbucks, Costa etc ever have a 'skin' on it? Just microwaved myself a milky coffee and it always has a skin on it. Is it because the mug is static in the microwave?

Why would it have a skin? It is freshly aerated hot milk, that's just been poured into the cup. It is frothy for a start and not been microwaved when non-frothy and un-stirred. A skin forms when heated milk cools without interference. Frothed milk that's been recently poured won't form a skin when cooling.

Thanks - why doesn't that milk form a skin once poured though? Is it because it is steamed milk and has air in it, rather than microwaved milk? Blimey - I learned nothing in science.

Anything that keeps the milk moving will interfere with a skin forming. So the bubbles popping in froth would disrupt it, and be froth itself would prevent a skin from forming as it wouldn't be a flat surface. Coffee shops use semi skimmed milk typically which is less likely to produces skin.

Try giving your milk a fast stir just before microwaving, see if it doesn't form a skin then.