Tofu is made by soaking dried soybeans, grinding them into a slurry, boiling that slurry to produce soy milk, and then curdling the milk with a coagulant to form curds. The curds are pressed into blocks, and the type of coagulant and amount of pressing determine whether you end up with silken, soft, firm, or extra-firm tofu. The process is surprisingly similar to cheesemaking, just with soybeans instead of dairy.
Soaking the Soybeans
The process starts with dried soybeans submerged in water, typically at a ratio of roughly one part beans to many parts water. At room temperature, soaking takes about six to eight hours or overnight. Warmer water speeds things up considerably. Research on optimizing soy protein extraction found that soaking at around 37°C (body temperature) cut the time nearly in half compared to cold soaking, while actually increasing the amount of protein pulled from the beans. Some traditional recipes call for soaking at 60°C for about six hours.
During soaking, the beans absorb water and roughly double in size. This softening is critical because it allows the beans to break down more easily during grinding, releasing more protein into the liquid. Beans that aren’t soaked long enough produce a weaker soy milk with less protein available to form curds later.
Grinding Into Soy Milk
The soaked beans are ground with fresh water to create a thick, creamy slurry. In small-scale production, this happens in a regular blender or stone mill. Commercial operations use industrial wet grinders that process the beans continuously. Some producers grind with hot water (around 100°C) to begin deactivating enzymes immediately, which improves flavor by reducing the “beany” taste that comes from a specific enzyme in raw soybeans.
After grinding, the slurry is strained through cloth or a fine mesh to separate the liquid soy milk from the solid pulp. This leftover pulp is called okara, and it’s far from waste. Okara contains roughly 28 to 30 percent protein, 8 to 10 percent fat, and significant dietary fiber. In China and Japan, it has been eaten as a side dish for centuries and is increasingly used in bread, noodles, and sausages to boost fiber and protein content. Commercially, though, most okara still ends up discarded.
Boiling to Remove Antinutrients
Raw soy milk contains compounds called protease inhibitors that interfere with protein digestion if consumed in large amounts. Boiling eliminates them. Heating soy milk at 100°C for about nine minutes effectively deactivates these inhibitors. Commercial producers sometimes use higher temperatures for shorter times: heating to around 143 to 154°C for under a minute accomplishes the same thing.
This boiling step also serves a practical purpose. It denatures the soy proteins, meaning it partially unfolds them so they’re ready to bond together when the coagulant is added. Without this step, the proteins wouldn’t clump into curds properly. The boiled soy milk is then cooled slightly before moving to the next stage.
Adding the Coagulant
This is the step that transforms liquid soy milk into solid tofu, and the choice of coagulant shapes the final product more than any other variable.
The three most common coagulants are calcium sulfate (gypsum), magnesium chloride (nigari), and glucono-delta-lactone (GDL). Each works differently. Calcium sulfate and magnesium chloride are mineral salts. They contain positively charged ions that act as bridges between protein molecules in the soy milk, pulling them together into a network of curds. Calcium sulfate produces the highest yield and creates a firm but tender texture with a mild flavor, which is why it’s the most widely used coagulant worldwide. Magnesium chloride reacts faster and more aggressively, creating a denser, slightly harder curd with a clean, slightly sweet taste. It’s the traditional coagulant in Japanese tofu-making.
GDL takes a completely different approach. Instead of using mineral ions, it slowly converts into a mild acid after dissolving in the warm soy milk. This gradual acidification, which unfolds over 40 to 60 minutes, gently lowers the pH until the proteins coagulate on their own. The result is the smoothest possible texture, which is why GDL is the standard coagulant for silken tofu.
For regular (non-silken) tofu, the coagulant is stirred into soy milk that has been cooled to around 70 to 85°C. The mixture is stirred briefly, then left undisturbed for 10 to 20 minutes while curds form and separate from the yellowish liquid whey.
Pressing the Curds
Once curds have formed, what happens next depends on the style of tofu being made. For firm and extra-firm tofu, the curds are scooped or poured into a cloth-lined mold with drainage holes. Weight or mechanical pressure is applied on top, squeezing out whey and compacting the curds into a dense block. More pressure and longer pressing time produce a firmer, drier block. Extra-firm tofu is pressed the longest, sometimes for 30 minutes or more, resulting in a dense texture that holds up well in stir-fries and on the grill.
Soft tofu is pressed lightly or briefly, retaining more moisture and yielding a delicate, custard-like block that still holds its shape when sliced.
How Silken Tofu Differs
Silken tofu skips the pressing step entirely. Instead of forming curds and then compacting them, the coagulant (usually GDL, sometimes combined with calcium sulfate) is mixed directly into warm soy milk, and the entire mixture is poured into its final container before it sets. The soy milk coagulates in place, in the package, producing an unbroken, custard-smooth block with no whey separation. This “in-container” method is why silken tofu has a uniformly creamy texture throughout, unlike pressed tofu which can have a slightly grainy structure from compressed curds.
After setting, the coagulated tofu is submerged in water, cut into blocks, and packed in water-filled tubs for sale.
Commercial Packaging and Shelf Life
In commercial production, freshly made tofu is pasteurized to extend shelf life. The standard method places packaged tofu into a hot water bath at 80 to 85°C for 10 to 20 minutes, which kills surface bacteria without significantly altering the texture. The tofu is then rapidly cooled and sealed in water-filled packaging. Water-packed tofu stored this way typically lasts one to two weeks refrigerated. Aseptically packaged silken tofu, sealed without water in shelf-stable cartons, can last months unopened at room temperature.
The entire process, from dry beans to finished block, takes roughly 18 to 24 hours when you account for soaking time. The active work, grinding through pressing, takes only about an hour. That simplicity is a big part of why tofu has been made in homes and small shops across East Asia for over 2,000 years, using nothing more than soybeans, water, and a coagulant.