How soy milk is made
Soy milk is tofu before it sets, made by grinding soaked beans in about ten times their weight in water.
- stations
- 6
- things upstream
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- raw sources
- 2
- step from the ground
- 1
The short version
Dry soybeans are soaked, then ground wet with plenty of water into a slurry. The slurry is boiled to sterilize it and disable a bean enzyme that causes a grassy off-flavor. A strainer removes the pulp, and the milk is blended with vitamins and sweetener before it goes into cartons for long shelf life.
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Soak the beans
Dry soybeans sit in water for at least three hours, sometimes overnight, until they swell. The longer a soak runs in cool water, the more time an enzyme has to turn bean fat into a grassy-smelling compound.
3 hours or longer
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Grind them wet
The swollen beans are ground with added water into a thick purée. Traditional soy milk uses ten parts water to one part beans by weight, which leaves a protein content between 1 and 4 percent.
10 parts water to 1 part beans
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Boil the slurry
The purée is held at or near boiling. Heat sterilizes it, switches off a protein that blocks digestion and deactivates the enzyme behind the beany smell. Factories add an anti-foaming agent at this stage because soy foams hard.
15 to 20 minutes
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Strain out the pulp
A filter or strainer removes the insoluble fiber, leaving a smooth white liquid. The leftover pulp is a by-product that is sold on for other uses.
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Sweeten and fortify
Sweeteners, flavors and added vitamins and minerals are blended in to make the product behave more like dairy milk.
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Seal in cartons
Finished soy milk is sold in plastic bottles or plastic-coated cartons such as Tetra Pak. Those cartons are what gave soy milk a long shelf life and let it spread worldwide.
Worth repeating
- Soy milk first entered the English language as soy-bean milk in an 1897 report from the US Department of Agriculture.
- Cornell researchers worked out in 1966 that an enzyme called lipoxygenase causes soy milk's beany flavor, then built a process to remove it.
- In Qing dynasty China, cooks found that heating soy milk gently for at least 90 minutes broke down sugars that cause gas.
Back to the ground
Follow every input upstream and soy milk starts as these 2 raw sources.
Keep walking
Sources
Cite this page: "How soy milk is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/soy-milk