Ingredient

Oat milk

Oat milk is oats blended with water, treated with enzymes, and strained. Those enzymes are why it tastes sweet without any sugar being added, and understanding them explains most of what oat milk does — including why it is the plant milk that behaves best in coffee and why homemade oat milk so often turns out slimy.

The enzymes, and why it tastes sweet

Oats are mostly starch, and starch has no flavour. Commercial oat milk is made by adding amylase enzymes to the oat slurry, which cut that starch into shorter chains and simple sugars — chiefly maltose.

That is why oat milk tastes noticeably sweet even when the label says no added sugar, and it is an honest label: no sugar was added, it was created from the oats' own starch. It is the same process that makes malt sweet and the same family of enzymes that koji uses.

The enzyme treatment also thins it. Untreated blended oats are thick and gluey, because intact starch absorbs water. Cutting the starch up gives a liquid that pours like milk.

This is exactly why homemade oat milk is so often disappointing. Without enzymes, and especially if you use warm water or blend for too long, the starch swells and you get something slimy. Blend briefly, with cold water, and strain well — and expect it to be thicker and less sweet than a carton.

Barista versions, and what is in them

Plain oat milk in coffee has two problems: it curdles, and it does not froth.

Curdling happens because coffee is acidic and hot. The proteins and other solids in oat milk destabilise under those conditions and separate into flecks. Barista formulations add small amounts of a buffer — usually a phosphate salt — which resists the pH change and largely prevents it.

Froth needs something to stabilise the bubbles, and dairy milk uses its proteins. Oat milk has fewer and different ones, so barista versions add extra fat — typically rapeseed oil — and sometimes an emulsifier, which together give a foam that holds.

Neither addition is sinister and both are why barista oat milk works and standard oat milk sometimes does not. If your oat latte splits, the formulation is the likeliest reason, followed by very hot or very acidic coffee.

The plant milks, and what each is good for

They are not interchangeable, and treating them as one category is how cooking with them goes wrong.

Oat

Sweet, creamy, mild, neutral in flavour. Best all-rounder for coffee, baking and sauces. Thickens slightly when heated because of residual starch.

Soya

Highest in protein of the common plant milks, which means it behaves most like dairy — it sets in custards, curdles predictably with acid, and froths reasonably. The best choice for anything relying on protein.

Almond

Thin, mild, faintly nutty, low in protein and fat. Poor in coffee, poor for anything that needs body. Good in a smoothie or on cereal.

Coconut

Tinned coconut milk is a rich cooking ingredient; carton coconut drink is a thin beverage. Two different products, constantly confused.

Cashew

Creamy and mild, good in sauces where its fat helps.

Rice

Very thin and very sweet. Limited use in cooking.

Pea

High protein, neutral, froths well. Behaves similarly to soya.

Cooking with oat milk

• In béchamel and white sauces, where it works well — its residual starch actually helps, and its sweetness is mild enough not to intrude.
• In baking, as a direct one-for-one replacement for milk in most recipes. Its sweetness may let you reduce sugar slightly.
• In porridge and soups, where its creaminess is an asset.
• In coffee, using a barista formulation, poured into coffee that is not scaldingly hot.
• With acid, cautiously. Adding lemon or vinegar will curdle it, which is fine when you are making a buttermilk substitute and unwelcome in a sauce.
• Not for a set custard. It has too little protein. Soya milk is the plant milk for that, or use a starch or setting agent.
• Not for making a plant "buttermilk" that behaves identically — it acidifies and thins rather than thickening the way soya does.

Common questions