Plant-based milks can be frothed, but not all of them are created equal.

Plant-based milks are everywhere, from oat, rice, and almond to classic soy. When frothing them with an espresso machine's steam wand, the balance between protein and fat is crucial. The protein traps air bubbles and creates a stable foam, while the fat adds a creamy texture.

Skimmed milk usually produces a light, fluffy foam because it has enough protein but less fat, and it lacks the velvety creaminess that fat provides. In general, plant-based milks don't handle heat as well as cow's milk, so it's best to heat them less to prevent curdling. Those containing emulsifiers, such as canola oil or xanthan gum, tend to give better results because they prevent the mixture from separating into fat and water, since milk is essentially fat emulsified in water.

Oat milk is usually a good choice: it's rich enough and retains steam well, creating a pleasant microfoam. Soy milk also foams well, but it's delicate and curdles above 54 degrees Celsius (130 degrees Fahrenheit), so it's best to start with cold milk and use it with low-acid coffees, which can cause it to separate. Almond milk also requires low temperatures and doesn't always have enough protein for a smooth microfoam.

Not all options work. Cashew milk is watery and separates easily, so if you manage to get it to foam, it ends up unpleasantly runny. Hemp milk doesn't form strong bubbles, curdles easily, and some people don't like its vegetable taste.

Coconut and rice flours are also unsuitable. Coconut flour doesn't have enough protein to steam properly, and if you manage to create a decent foam, it quickly falls apart. Rice flour lacks sufficient protein and fat to cook effectively when steamed.

Since there are so many brands, it's difficult to make definitive recommendations. For optimal foam, the safest option is a barista mix.