Soy milk (duyu)

A bean drink, not a filtered milk

Duyu is a Korean soy drink made by cooking whole soybeans and blending them with cold water, sesame and a little salt. Unlike the filtered soy milk that is the first step of tofu, the Korean drink is not strained in the recipe, so the fibre and the bean skins remain in it. The drink is thick and creamy, and it is served at once, while the sesame gives it a toasted, nutty note.

The distinction matters for the rest of the kitchen. Tofu and yuba depend on a milk with a known solids content and a filtration, and this drink has neither. The Vitamix variant in the sources strains its drink through a bag or fine sieve after blending, which gives a smoother, thinner milk, but it is a different product.

Soaking and cooking the beans

Two cups of dried soybeans, about 360 g, are washed and soaked in cold water for 10 to 12 hours. The soaked beans are drained, added to a large pot of boiling water, and boiled uncovered over medium-high heat for 15 minutes, stirring now and then. The heat is then reduced to very low, the pot is covered and the beans simmer for five minutes.

The beans are strained, rinsed under cold running water, drained well and cooled. The cooked beans keep for the drink in a zip-lock bag in the freezer, but the source gives no keeping time for them. Half a cup of the cooked beans is used for each batch of the drink.

Why the heat comes first

The FAO bulletin on soybean products notes that trypsin inhibitors in raw soybeans reduce digestibility, and that heat starts their inactivation. The cook in this recipe is therefore part of the safety and digestibility of the drink, not only a way of softening the beans. The recipe's boil and simmer are the controls the page gives, and it does not state a temperature for them.

The blending is done after the cook and on cooked beans, with the cold water added at the start. Maangchi's recipe blends the beans with their skins, so no straining step is given. The drink is served as soon as it is blended.

A machine variant and its limits

Vitamix's soy milk recipe steams the beans for 15 minutes, blends 260 g of cooked beans with 960 mL of water for 60 seconds, and offers an optional straining step. It is a method variant of the same bean-and-water drink, and the Korean recipe is not merged with it. The Vitamix recipe is a commercial appliance's recipe, and its steaming and blending are not the stovetop boil described above.

Storage and open questions

The recipe says to serve the drink immediately, and no keeping time is given for it in the sources. The yield of the drink is not printed, and the solids content of the unstrained drink has not been measured. The Korean history of duyu was not researched for this page; the Chinese history of soy milk is a separate matter, and the earliest reference given for it is not evidence for this drink.