It is very annoying when you add soy milk to your coffee and it goes funny.
There are two reasons why the soy milk curdles:
If you favour a more acidic coffee (like many African coffees), it's more likely to curdle.
So soy milk + a hot light-roasted coffee = cheesy-looking soy milk.
Don't worry, though – there's a solution.
And if you're making a big pot of coffee at home, dilution is your friend.
Jeremy Challender says: "Curdling's less likely to happen in a more diluted beverage, so if you did a big 60g/litre pour-over, the pH will be a bit higher than if it was a super strong stove-top espresso. So slightly more dilution should help with your coffee at home."