Microfoam

The decorative application of microfoam is called latte art, which involves making patterns in espresso-based drinks.

Microfoam is essential for this as the microscopic bubbles give definition and stability to the patterns, which are harder to achieve with macrofoam which disperses more readily.

Latte macchiato is another drink which generally has separate layers of dry foam and liquid milk, but microfoam is occasionally used instead.

Microfoam may also be added to brewed coffee in a café au lait, and faint latte art can be produced.

As it requires a skilled barista to produce microfoam (especially when used for latte art), it is a sign of attention to quality, and a defining characteristic of the third wave of coffee.

[6] The interaction between fat and air creates a structure of microscopic bubbles strong enough to support itself, and even be submerged (i.e. suspended within the liquid milk).

[citation needed] This can be shown trivially by adding various quantities of skim milk powder which contains a high concentration of β-lactoglobulin.

[15] Whilst this is true, an excessive fat constituent also enables larger bubbles, leading to macrofoam rather than microfoam.

[13] However, microfoam tends to separate into layers more quickly than it reduces in volume, so baristas usually steam milk immediately before serving it.

When using a steam wand, a slight but audible hissing sound occurs when the air enters the milk, mainly due to microscopic cavitation.