For a good cup of coffee, what you want is froth and creaminess. To know which milk alternative is best in coffee, we need to look at the chemical compositions of the milk because, notes Pieters, “Milk of different compositions will have different steaming temperatures for optimal heating and sensory goals.” The milk alternative that is closest to cow’s milk and best for coffee if you don’t mind the taste, is soy milk, but you need to keep it to below 62°C.
Frothiness
This is dependent on the protein content. The higher the protein content, the creamier foam you’ll get with bigger air bubbles.
Sweetness
In cow’s milk, this is dependent on the lactose content. When lactose is heated, the Maillard effect causes sweetness to be created in the milk. For milk substitutes, this will depend on whether sugar has been added or, as in the case of oat milk, the milk alternative is already naturally sweet.
Foam stability
This is dependent on the fat content. Low fat content allows for stable foam at higher temperatures, whereas higher fat content provides stable foam at or below room temperatures.