Together with our friends from "Physics for Everyone," we dive into the world of coffee in a scientific way!

What is foam from a physics point of view?
Essentially, it's millions of air bubbles trapped in thin films of milk.

It's precisely thanks to milk that coffee foam lasts longer than ordinary foam (soap foam, for instance). When a barista steams milk, air gets drawn inside it. Proteins line up around the bubbles, reduce the surface tension and make the shell more elastic. All of this works like a kind of shape-holding framework that keeps the bubbles from merging and popping right away.

Fats make the foam softer and creamier. The right temperature also plays an important role, because milk that's too cold whips poorly, while milk that's too hot destroys the protein structures.

Good milk foam, made correctly, settles more slowly, holds the aroma longer and reveals the flavour of your favourite coffee more harmoniously. 

Physics, and no magic at all!