Milk contains lactose, and heat makes it more perceptible — up to a point.
The curve
Cold milk tastes mildly sweet.
Warming to about 60 to 65 °C increases perceived sweetness noticeably. This is the window, and it is why properly steamed milk tastes sweeter than the same milk cold.
Past about 70 °C the lactose starts degrading and proteins denature further. Sweetness drops away and the milk tastes flat, cooked, sometimes faintly eggy.
The commonest mistake
Deliberate overheating. People want a drink that stays hot, so they push the temperature — and lose exactly the quality they were steaming for.
Warm the cup instead. A preheated cup keeps a 62 °C drink hot far more effectively than overheating the milk does.
Judging it
Hand on the side of the jug. Stop when it becomes uncomfortable to hold. That is around 60 to 65 °C for most people.
The other causes
Old milk. Milk near its date has begun to sour and will never taste sweet.
Skimmed milk. Less fat means less roundness, and the sweetness reads thinner.
Plant milk. Standard oat and soy have far less sugar than dairy; barista editions often add some.
Last reviewed 8 August 2026