Nearly every coffee machine has the milk go through this device which not only heats it up but causes it to froth up.

Why is this important for a coffee? What's wrong with just heated milk?

  • 1
    It's an important component of the "mouth-feel" of coffee. It's why coffee from an Aeropress tastes different from say something brewed using an espresso machine.
    – seeker
    Aug 5, 2015 at 13:50
  • Have you ever tried a cappuccino with frothed milk and one with only heated milk side by side? Aug 9, 2020 at 13:00

2 Answers 2


When heating milk with steam, aerating the milk (the process of drawing in air which creates foam) is essential to allow the milk to heat gently, without scalding. If you're using some other heating process, you'll have to take care of preventing scalding in some (other) way.

An extra benefit of foam — particularly microfoam where the bubbles are too small to see — is that it changes the surface tension of the liquid beverage, potentially allowing more taste-buds to come into surface contact. So you get more flavor bio-chemically. As (good) baristas know, tiny bubbles taste better than big ol' soap bubbles. This theory explains why.


It's not that just heated milk is wrong or tastes bad. It's only that there are some (popular) coffee drinks that uses steamed or frothed milk (are not the same, read this) by traditional way.

On those popular drinks you can find the cappuccino, latte, etc... (as you can see on this infographic), but at home you always can add regular hot milk to your coffee (but we all agree that it isn't feel and taste like the regular way).

Last, why are those techniques important for a coffee? I think that gives a different flavour and tasting to the drink, due to its consistency (and of course, that let you to do some pretty nice latte art)

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