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Why does my soy milk curdle in coffee?

Why does my soy milk curdle in coffee?

Does soy milk have beef with specialty coffee?

Are you a soy drinker? Have you ever been served a chunky brew? Have you ever made yourself a soy latte and it had a consistency that meant you had to eat it with a spoon?

You could be mistaken into thinking that the soy milk is off. But what is the more likely scenario?

Initially soy milk was the only option as far as alternative milks went and it wasn't formulated to be Barista friendly- it did not like to be heated. Baristas wanted a soy that could stretch like cows milk, with a creamy, velvety texture and be able to reach that sweet spot of 60 to 65 degrees Celsius without turning into scrambled tofu.

Only then did we welcome a variety of Barista Soy options and now there are so many. But sometimes the soy still doesn't want to play ball and you end up with a cup full of chunks. 

There are 2 factors which are the likely cause of this issue. Soy is rich in protein. The proteins in soy milk are sensitive to the lower PH of Coffee and that can cause proteins to denature and look curdled. Coffee can be further down the PH scale- the lighter the roast, the more acidic it can be. Put the two together and boom! Chunks.

Soy milk being steamed on an epresso machine then being poured into coffee in a glass latte cup. It then curdles


You can work with your roaster to find a blend that will work with your chosen soy. The other thing which is worth checking is the temperature the soy is being heated to. Never overheat soy past 65 degrees- unless you are making tofu.

Finally- it is worth checking your ratio and recipe. Don't be tempted to try using a ristretto. That sour, salty vibe is not going to pair nicely with soy. If you are really struggling to combine the two you can blend them by pouring the extraction into the steamed soy milk. Yes that means no latte art, but it does give you a more consistent result.

Until next time- keep sipping delicious brews.