What type of milk tends to foam the best and provides a stable structure?

Whole milk is considered to foam the best and provides a stable structure due to its balanced composition of fat, proteins, and sugars. The presence of fat in whole milk contributes to a creamy texture and helps create a more stable microfoam when steamed. The milk proteins, particularly casein and whey, are essential for stabilizing the foam, and the fat content helps trap air, resulting in a rich and velvety texture that holds up well in beverages like lattes and cappuccinos.

In contrast, skim milk has a lower fat content, which can lead to less creamy foam and a more airy texture that might not be as stable as that produced by whole milk. Low-fat milk, while offering some benefits, still lacks the richness of whole milk, potentially leading to a less satisfying foam quality. Non-dairy milks have diverse compositions depending on the source (such as almond, soy, oat, etc.), and while some can foam well, they generally do not match the performance of whole milk in terms of stability and texture across all types. Whole milk strikes the optimal balance that baristas seek for frothing, making it the preferred choice for achieving excellent foam structure in espresso-based drinks.