Ingredient

Soya milk

Soya milk is the plant milk with real protein in it, and that single fact is why it behaves more like dairy than any of the others. It sets in a custard, it curdles predictably with acid, it froths, and it is what tofu is made from — all of which are protein doing what protein does.

Protein is the whole difference

Soya milk contains substantially more protein than oat, almond, rice or coconut milk — comparable, in many formulations, to dairy milk.

That protein does everything the other plant milks cannot. It coagulates with heat and with acid, which is why soya milk can be turned into tofu with a coagulant and why it curdles reliably when you add lemon juice — useful when you want a plant buttermilk, and a nuisance in coffee. It sets a custard, holding a gel the way egg and dairy proteins do. It stabilises foam, so it froths.

It also means soya milk thickens when heated and forms a skin, in the same way dairy milk does. Yuba, the skin lifted off simmering soya milk, is a delicacy in Japan and China and is made of exactly that.

The trade-off is flavour. Soya has a distinct beany note that some formulations reduce and none entirely removes, and it is more assertive than oat or almond in a delicate dish.

What it is best for

• Custards, panna cotta and set desserts, where its protein does the setting. The only common plant milk that reliably manages this.
• A plant buttermilk — soya milk with lemon juice or vinegar thickens and curdles convincingly, which oat milk does not.
• Coffee, where it froths better than almond, though it curdles more readily than barista oat in very hot acidic coffee.
• Béchamel and savoury sauces, where its body is an asset and its beany note is covered.
• Baking, as a direct substitute for dairy milk.
• Tofu and yuba, if you are making them, which requires unsweetened, unflavoured soya milk with a high solids content.
• Soya yoghurt, which cultures much like dairy yoghurt because there is protein to set.
• In East Asian cooking, where it is a drink and an ingredient in its own right rather than a substitute for anything — sweet or savoury soya milk with youtiao for breakfast, for instance.

Buying it

Unsweetened

What you want for cooking. Sweetened soya milk in a savoury sauce is a mistake you make once.

Sweetened / original

For drinking and cereal.

Solids content

Look at the protein figure. Higher-protein soya milks behave better in cooking, and the range between brands is significant.

Fortified

Most are, with calcium and vitamins. Organic versions frequently are not, which is worth knowing if that is why you are buying it.

Allergen

Soya is one of the fourteen allergens that must be declared in food sold in the UK.

Flavour

Brands differ considerably in how beany they taste. It is worth trying more than one before deciding you dislike it.

Stopping it curdling in coffee

The protein that makes soya milk useful everywhere else is exactly what makes it split here. These help, in rough order of effect.

1. Take the coffee off the boil. Freshly boiled water is the biggest single cause — let an espresso or a brew stand for half a minute.
2. Warm the soya milk before it goes in. A cold milk hitting hot acidic coffee is the worst case; a warmed one is far more stable.
3. Pour the coffee into the milk rather than the milk into the coffee. It sounds like superstition and it is not: it dilutes the acid gradually rather than dropping a little milk into a lot of acid.
4. Use a barista formulation, which contains a buffer that resists the pH change.
5. Use a less acidic coffee. Light, fruity, high-acidity roasts split soya milk far more readily than darker ones.
6. If it has already flecked, it is a cosmetic problem rather than a spoiled drink — the proteins have coagulated, not gone off.

Common questions