Soy Milk Glycine max
The one plant milk with enough protein to set like dairy in a custard.
In the kitchen
Under heat
It has enough protein to actually thicken and set with heat, unlike other plant milks — the closest substitute to dairy in a custard for that reason.
Against air
Opened, it behaves close to dairy milk — a skin forms on top if left uncovered while hot.
In storage
Same as dairy once opened: coldest part of the fridge, sealed, used within about a week.
At the shop
Unsweetened, plain is the only version worth keeping in a savory kitchen — sweetened versions will throw off anything but a smoothie or dessert.
Which variety, for what
- Unsweetened, plain
- The closest substitute to dairy milk by protein content — the one to reach for in cooking.
- Barista blend
- Adjusted specifically to foam for coffee, the same idea as the almond-milk version.
Beyond the kitchen
TOFU IS CURDLED SOY MILK
Tofu is made by coagulating soy milk with a salt — nigari, or calcium sulphate — and pressing the curds, structurally the same operation as cheesemaking. Soy milk is the intermediate step, and in East Asia it was drunk as a by-product of tofu making for centuries.
DOUJIANG AND YOUTIAO
Hot soy milk with fried dough sticks is a standard northern Chinese breakfast, often served savoury with vinegar, soy sauce and pickles rather than sweet. The savoury version curdles deliberately into a soft custard.
IT FOAMS AND IT SPLITS
Soy proteins make it the best non-dairy milk for latte art, but they also coagulate in acid — which is why soy milk curdles in coffee. Barista formulations add acidity regulators specifically to stop this.
MOST SOY IS NOT EATEN BY PEOPLE
The great majority of the world soy crop goes to animal feed and to oil, with only a small fraction consumed directly as food. Soy milk, tofu and tempeh are a minor share of a crop that mostly exists to produce meat.
A longer history
Soybeans were domesticated in China, most likely in the north-east, several thousand years ago, and became one of the five sacred grains. Tofu is traditionally dated to the Han dynasty, and while the attribution to Liu An is legendary rather than documented, tofu production is well established in China by the Tang and Song periods and spread from there to Korea, Japan and Southeast Asia.
Soy milk existed throughout that history as the stage before tofu and as a drink in its own right, particularly in northern China, where hot doujiang is a breakfast staple. The first commercial soy milk businesses in Asia date to the early twentieth century, and Hong Kong's Vitasoy, founded in 1940, made it an industrial beverage.
It reached Western markets mainly through health food shops in the 1970s and 80s and became a mainstream supermarket product in the 1990s, for a long time the default non-dairy milk before almond and oat overtook it. Its long East Asian history is much older than its Western one and belongs to a completely different culinary logic.