A multitude of foam consistencies are used in the preparation of foods and beverages. Chefs use foams in cooking because they make taste sensations last longer; the flavour sits between the bubbles in a foam and makes its way to your taste buds as if through a maze. In filter coffee (served black, no milk) flavour takes a direct route to the palate. But with a latte, flavour compounds must slide over a complex matrix of thousands of bubbles until they reach taste receptors on the tongue. This means microfoams produce flavour sensations that last long and are light in taste and texture.
Chocolate mousse features large, closed-cell foam bubbles (each cell occupies a distinctly separate pocket, surrounded by solid material), as does yeasted bread dough. After the dough is baked into bread, its bubbles form an open-cell foam. You know this by the way water immediately soaks into the bread. Similarly, if you dunk a biscuit or cookie into your coffee, liquid almost immediately penetrates the biscuit. The foam we like to use for latte art has a structure that is finer and more complex than that of these large-cell foams.
If you manipulate the components in milk and rearrange the concentrations of its protein, fat, sugar, and water, it’s possible to make a foam that’s so compact, with such tiny bubbles, that it could take 24 hours for the liquid to separate from the bubbles. The tinier the bubbles, the longer it takes for this separation process to finish. This process is known as drainage. For latte art purposes, we don’t necessarily want absolutely microscopic bubbles. Professor Steven Abbott has composed a list of factors necessary for producing latte art–conducive microfoam.
Professor Abbott’s Five Foam Factors
- Wet (i.e., having a high and/or liquid fraction)
- Fine bubbles (of small diameter)
- Stable for minutes at relatively high temperatures (Ensures latte art and ~55° C (131° F) serving temperature can co-exist)
- Moderate viscosity (for a luxurious feel)
- Low yield stress (for easy pouring)
As we examine foams throughout this chapter,