(updated October 13th, 2026)
Yes. Soy is the plant milk that behaves most like cow’s milk in a cappuccino, because it’s the only common one with a similar amount of protein. It froths well, and in a 2024 study of eight milks it was one of the three best plant milks for foaming. The catch is that it can curdle in hot coffee, which is easy to prevent once you know why it happens.
Does soy milk froth well?
Yes, and the reason is protein. A Swiss comparison of 27 plant drinks found that cow’s milk and soy drinks were the only ones with more than 3% protein; most other milk alternatives had 1% or less. As two University of Queensland researchers explain in The Conversation, soy’s proteins are also ball-like, like those in cow’s milk, which makes them “good for foaming”. So soy is the one plant milk where the protein story behind dairy foam carries straight across.
In that 2024 study, published in Soft Matter, soy was one of the three best plant milks for foaming, alongside oat and pea. Hot, cow’s and goat’s milk still made more foam; cold, soy beat cow’s milk on both foam volume and how long the foam lasted. Oat made the longest-lasting foam overall.
How do you make a soy milk cappuccino?
- Pull a shot of espresso into a small cup, or make a strong coffee without a machine. Let it sit for a minute before the milk goes in.
- Start with cold soy milk, about 100 ml for a classic-sized cappuccino. A barista version will curdle less.
- Froth it with a steam wand, a handheld frother or a French press until it’s glossy and roughly doubled.
- Keep it warm, not hot. Stay within the 55 to 65°C (139 to 149°F) range baristas use for dairy, as Perfect Daily Grind reports from the Specialty Coffee Association. Hotter makes curdling more likely.
- Pour it over the coffee and spoon the foam on top.
Why does soy milk curdle in coffee?
Heat, mainly, with the coffee’s acidity helping it along. Researchers at the University of Strathclyde studied exactly this, mixing soy milk into coffee at different temperatures and strengths. They found the “curdling” is a separation that happens at high temperature and not at low, and that it’s reversible: the mixture came back together when it was cooled or when more soy milk was added. They used instant coffee, but the practical fixes follow directly:
- Let the coffee cool for a minute before adding the soy milk.
- Don’t overheat the milk when you froth it.
- Add more milk if it starts to split; in the study, that brought it back together.
- Use a barista soy milk, and check the label for an acidity regulator such as dipotassium phosphate. Oatly, for one, adds it to its barista oat milk to stop it separating in hot drinks.
Does it work for cold foam?
Yes, and it’s one of the better choices for it. Frothed cold, soy beat cow’s milk in the Soft Matter study, and cold drinks avoid the curdling problem altogether. Froth it cold and spoon it over an iced cappuccino.
How many calories does it add?
Unsweetened soy milk sits between skim and 2% dairy milk, as the table of calories by milk type shows. Sweetened and barista versions often add cane sugar, so check the label if that matters to you.
Should you use it for a cappuccino?
If you want a dairy-free cappuccino with the most body and protein, yes. It foams about as well as oat, though oat’s foam lasts longer, and it’s the closest plant milk to cow’s milk for protein. Just let the coffee cool slightly first, or it may split. If curdling keeps catching you out, oat milk is the easier option.
