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How to steam perfectly silky soy for your coffee

As specialty coffee ambassadors it is very important to us to serve the best coffee possible using whatever milk our customers prefer – full cream, skim, almond or soy. As more and more people choose to drink their lattes and cappuccinos with soy we’ve been challenged to become soy masters. And we want to pass on our tips so you can become a soy master too. We know you want to!

But first let’s look at two of soy’s enemies.

Soy’s enemy no 1 – acid

Soy 2

Being specialty coffee roasters we play a fine balance of roasting for full coffee development while trying to maintain the coffee’s natural terroir character.

One of our goals is to retain more fruit character in our beans, which causes the coffee’s natural malic and citric acids to be displayed in the cup. Now while these flavours are wonderful and very satisfying, they are not so kind to soy. Yes acid is soy’s nemesis!

Soy is full of proteins which reacts with acid and disrupts the balance of these proteins. This is what causes the clumping and the curdling you have seen from time to time in a poorly made soy latte. Think of it as a power balance. When the proteins are in power we achieve a perfectly silky soy latte, but when the acid gains power we get curdling.

Our White Knight Espresso Blend is perfectly suited for soy coffees. It’s roasted a touch darker than our single estate coffees to ensure a softer acidity and is the perfect partner for your soy latte.

Soy’s enemy no 2 – heat

soy 3

Another influential element in preparing a perfectly textured soy coffee is the temperature. Soy is particularly sensitive to heat which causes the proteins to degrade. So when we heat soy we lower the protein level which impacts the balance of protein to acid. If you heat the soy too high you will get, you guessed it, a curdled soy latte.

We train all our baristas to steam soy between 55-60 degrees celsius. This ensures we retain enough protein and keeps the acids and the proteins in balance.

Tips for steaming soy


So now we know we need to keep the proteins and acids in balance and not to overheat soy. But we have a few more tips which we’ve learned from making thousands of soy lattes and cappuccinos. Here they are.

  1. Follow our general guidelines for steaming milk here.
  2. If you want consistency use Bonsoy. This is the brand we use in all our cafes and it is more consistent than any other brand we’ve tested.
  3. Be gentle and do not introduce too much air into the soy when steaming. This will ensure it remains silky and perfectly textured. This is where a lot of people come unstuck as they seek to create too much microfoam.
  4. If you are finding the soy curdling try lowering the temp of the soy by turning off the steam earlier.
  5. When pouring soy into the extracted coffee do it reasonably fast and consistently. This will evenly combine the coffee and soy protein. If you introduce the soy too slowly you risk the coffee and soy protein reacting and will curdle.
  6. Use blends over single estate coffee beans. Blended coffees are commonly roasted darker which creates a softer acidity and reduces the risk of reacting with soy.
  7. Ensure the soy is cold from the fridge not room temp just off the shelf.

I hope these tips are helpful in helping you steam perfectly silky soy.

Keep it special.



  1. I just can’t do my coffee with soy, but I’ve been struggling to get the texture right for the occasional Chai latte. Your tips have been revolutionary! Keep up the wonderful work.

  2. Thank you. I’ve just started making my own soy milk and it curdled where as the store bought stuff doesn’t. Can’t wait to try.

  3. I don’t suppose you have any secret tips for using Bonsoy in a Nespresso frother? (I know this won’t be a popular question but thought I’d ask anyway!). When I try, it always ends up with thick foam rather than silky. Thanks!

    1. Hi Amy, that is a great question. We have never used a Nespresso frother, but … re ending up with thick foam rather than silky … you could always pour the heated textured milk into a jug (after using the Nespresso frother) and swirl around to try to re-combine the froth into the milk before using. This could possibly make the milk silkier, more like runny paint. Or you could pour some of the froth out and then again swirl before using. Hope that makes sense.

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