Dairy and plant-based milks under steam

Every milk behaves differently under a steam wand because protein and fat content — not just flavor — determine how it foams. Whole dairy milk is the reference point: its proteins and fats stabilize a dense, glossy microfoam and it's the most forgiving milk to steam. Skim or low-fat milk foams more in volume but the foam is drier and less stable, since there's less fat to hold it together, and the resulting drink can taste thinner.

Oat milk (barista-formulated versions especially) behaves closest to dairy among the alternatives — creamy body, holds latte-art contrast well, and is generally heat-tolerant across normal steaming temperatures. Almond milk has lower protein, which makes its microfoam less stable and more prone to splitting (visibly separating) at higher temperatures — it steams best gently and toward the cooler end of the normal range. Soy milk can curdle if it's not fresh or if it meets high-acid espresso at too high a temperature — steam it gently and use fresh stock.

Coconut milk has low protein and foams thinly, and its distinct flavor can compete with delicate origin notes, so it's often chosen more for taste than for texture. Pistachio and other nut milks generally behave similarly to almond — lower protein, less stable foam, best steamed gently. The single biggest variable with plant-based milks is brand and formulation, far more than with dairy — a milk labeled "barista" or "barista edition" is specifically formulated to behave like dairy under heat, and is usually worth the difference for milk-forward drinks.