From Soybeans to Tofu and Bean Curd Skin

What is tofu and how is it made from soybeans?

Tofu is a soft, cheese-like food made by curdling fresh soy milk and pressing the curds into blocks. The process starts with dried soybeans, which are soaked, ground with water, and cooked to produce soy milk. A coagulant is then added to separate the milk into solid curds and liquid whey. The curds are gathered and pressed to form tofu, while the leftover soybean pulp, called okara, is often used in other dishes. Bean curd skin, also known as yuba, is the thin film that forms on the surface of soy milk when it is heated; it is lifted off and dried.

The texture of tofu ranges from silky and custard-like to firm and dense, depending on how much water is pressed out and which coagulant is used. Tofu is a staple in many Asian cuisines and is valued for its mild flavor and ability to absorb sauces and seasonings.

The tofu making process step by step

Making tofu at home or in a factory follows a similar sequence, though equipment and scale differ. Below are the essential steps.

1. Soaking the soybeans

Dried soybeans are rinsed and soaked in plenty of cold water for 8–12 hours, or overnight. The beans double in size and soften, which makes them easier to grind. In warm weather, the soaking water may be changed once to prevent fermentation. For a quicker method, beans can be soaked in hot water for 2–3 hours, but the traditional slow soak yields a smoother soy milk.

2. Grinding with water

The soaked beans are drained and ground with fresh water into a thick slurry. Traditionally, a stone mill was used; today, a high-speed blender or a dedicated soy milk maker works well. The ratio is typically about 1 part dry beans to 3 parts water, but this can be adjusted for richer or lighter soy milk. The result is a frothy, pale beige liquid containing all the bean solids.

3. Cooking the slurry and straining to get soy milk

The slurry is heated to a gentle boil and simmered for 5–10 minutes, stirring frequently to prevent sticking and boiling over. Cooking improves flavor, destroys enzymes that hinder digestion, and helps the proteins coagulate later. The hot mixture is then strained through a fine cloth or mesh bag. The liquid that passes through is fresh soy milk; the fibrous solids left behind are okara. Okara has a mild, nutty taste and is used in patties, baked goods, or as animal feed.

4. Coagulating the soy milk

The soy milk is cooled to about 70–80°C (160–175°F) and a coagulant is stirred in. Common coagulants include:

• Nigari (magnesium chloride): produces slightly sweet, firm tofu with a clean taste.
• Gypsum (calcium sulfate): yields tender, high-calcium tofu; widely used in Chinese-style tofu.
• Glucono delta-lactone (GDL): an acid coagulant that creates very smooth, silken tofu, often used for boxed silken tofu.
• Lemon juice or vinegar: possible but less common; results in a slightly sour, softer curd.

The amount of coagulant is small: about 2–3 grams per liter of soy milk. The mixture is left undisturbed for 15–30 minutes, during which the proteins bond and form delicate white curds in a clear yellowish whey.

5. Pressing the curds

The curds are ladled into a mold lined with cheesecloth. For firm tofu, the cloth is folded over and a weight is placed on top; the pressure squeezes out whey and compacts the curds. Pressing time and weight determine the final texture: 15–30 minutes with moderate weight gives soft or medium tofu, while 1–2 hours with heavier weight yields firm or extra-firm tofu. For silken tofu, the curds are not pressed at all; they are simply scooped into containers and cooled, retaining a high water content.

Tofu production process in a factory

Industrial tofu production automates each step for consistency and efficiency. Soybeans are cleaned, soaked in large tanks, and ground continuously. The slurry is cooked with steam and separated by centrifugal filters or screw presses to extract soy milk and remove okara. The soy milk is then precisely heated and coagulant is injected inline; the curds form in a continuous stream and are cut into slabs. For firm tofu, curds are transferred to automated presses that apply uniform pressure; for silken tofu, the soy milk and coagulant are mixed directly in the final package, which is then heat-sealed and pasteurized. Factory-made tofu is usually packaged in water-filled tubs or vacuum packs and kept refrigerated.

Silken tofu production process: a closer look

Silken tofu, also called soft or Japanese-style tofu, has a delicate, custard-like texture and a high moisture content (about 90% water). Unlike regular tofu, it is not pressed. The process is:

1. Prepare a rich soy milk (usually with a higher bean-to-water ratio, around 1:5).
2. Cool the soy milk to about 20–30°C (68–86°F) if using GDL, or keep warm (70–80°C) for nigari or gypsum.
3. Dissolve the coagulant in a little water and stir it into the soy milk thoroughly.
4. Pour the mixture into heat-proof containers or molds.
5. Heat the containers gently in a steamer or water bath (80–90°C) for 20–30 minutes to set the curd without disturbing it.
6. Chill the tofu in the refrigerator for at least 2 hours before unmolding.

The result is a smooth, jiggly block that breaks easily. Silken tofu is ideal for smoothies, desserts, miso soup, and cold dishes like hiyayakko, where it is topped with soy sauce and scallions.

Comparisons: Firm vs. silken tofu and other soy products

Bean curd skin: the bonus from soy milk

When soy milk is heated in a shallow pan, a protein-lipid film forms on the surface as water evaporates. This film is bean curd skin or yuba. It is lifted off with a stick or chopsticks and dried flat or in bunches. The skin has a rich, slightly sweet soybean flavor and a tender-chewy texture. It can be used fresh in salads or soups, or rehydrated from dried form for stir-fries and braises. Bean curd skin is a good source of protein and is prized in vegetarian cooking for its meaty bite.

Tips for making tofu at home

• Use high-quality, food-grade dried soybeans; old beans may not produce as much milk.
• Strain the soy milk well; leftover pulp will make tofu grainy.
• Temperature control is key: too hot and the curds become tough; too cool and they won't form.
• For beginners, gypsum or GDL is easier to work with than nigari.
• Line the mold with cheesecloth and press gradually; sudden heavy weight can trap whey and cause a crumbly texture.
• Silken tofu does not need pressing, but the container must be heat-proof and tightly covered to prevent water droplets from marring the surface.