Tofu is made by soaking dried soybeans, blending them into a slurry, boiling and straining that slurry into fresh soy milk, then adding a coagulant that causes the proteins to clump into curds. Those curds are scooped into a mold and pressed until they hold together as a solid block. The entire process mirrors cheesemaking: you start with a liquid rich in protein, trigger that protein to solidify, then shape the result.
Soaking and Blending the Beans
The process starts with dried white soybeans soaked overnight in water. This softens them enough to blend smoothly. After soaking, the beans are blended with an equal amount of the soaking liquid to create a thick, gritty slurry. At this stage, everything is still raw, and the mixture has a strong beany flavor that cooking will mellow out.
Making Fresh Soy Milk
The slurry is heated just to a boil, then strained through a cloth or fine mesh to separate the liquid soy milk from the fiber (called okara). This straining step is what distinguishes tofu from other soy products. You want a smooth, clean liquid with as much dissolved protein as possible, because that protein is what will eventually become your tofu.
After straining, the soy milk is simmered gently for 10 to 15 minutes. This does two things: it cooks off raw flavors and concentrates the protein, which leads to better curds later. Constant stirring during this step prevents scorching on the bottom of the pot.
How Coagulants Turn Liquid Into Curds
This is the step that actually creates tofu. Once the soy milk comes off the heat, a coagulant is stirred in. The coagulant neutralizes the electrical charges that keep soy proteins suspended in liquid. When those charges drop, the proteins stop repelling each other and begin clumping together through a combination of chemical bridges, bonds between sulfur-containing parts of the protein, and attraction between water-repelling surfaces. The result is a network of protein that traps water inside, forming soft, white curds floating in a yellowish whey.
With mineral salt coagulants like nigari (magnesium chloride), the magnesium ions physically link protein molecules together by connecting to specific sites on their surfaces, forming bridges between them. With acid coagulants like lactic acid or vinegar, the mechanism is different: the acid lowers the pH toward the point where soy proteins carry no net charge (around pH 4.0 to 4.5), which removes the repulsion that kept them apart. These two different pathways produce noticeably different textures in the finished tofu.
Choosing a Coagulant
The coagulant you use shapes the flavor, texture, and firmness of the final block more than almost any other variable. Here are the most common options:
- Gypsum (calcium sulfate): The most versatile coagulant. It produces lofty curds, a slightly sweet flavor, and works well for both soft and firm tofu. This is the traditional choice in much of Chinese tofu making.
- Nigari (magnesium chloride): Coagulates faster and produces smaller, tighter curds, resulting in firmer tofu with a slightly bitter edge. This is the traditional Japanese coagulant, derived from seawater.
- Glucono delta-lactone (GDL): An acid that works slowly and evenly, producing a jelly-like, custard-smooth tofu. This is commonly used for silken tofu.
- Vinegar or lemon juice: Readily available but less forgiving. These acids create small, grainy curds and slightly sour, crumbly tofu.
- Fermented whey: A traditional acid coagulant where lactic acid makes up more than 55% of the active ingredient. It produces soft-textured tofu with a distinctive tang.
Calcium sulfate tofu tends to have a harder texture and a higher proportion of certain protein types (specifically the 11S fraction), while acid-coagulated tofu retains more of the 7S protein fraction and stays softer. In practical terms, if you want one coagulant that covers the widest range of tofu styles, gypsum is the best starting point.
Forming and Pressing the Curds
Once curds have formed, they need about 15 minutes of resting to fully separate from the whey. Then the curds are gently scooped with a slotted spoon into a tofu mold, which is typically a box with small drainage holes lined with cloth. A weight of 2 to 3 pounds is placed on top, and the curds are pressed for anywhere from 20 minutes to 2 hours depending on how firm you want the finished block.
A short press with light weight produces soft tofu that’s delicate and high in moisture. A longer press with heavier weight squeezes out more whey and creates the dense, sliceable blocks sold as firm or extra-firm tofu. The coagulant choice and pressing time together determine where the tofu lands on that spectrum.
How Timing Breaks Down
From start to finish, homemade tofu takes roughly a full day if you count the overnight soak, but only about an hour of active work. Soaking runs 8 to 12 hours (or longer). Blending and straining take about 15 minutes. Simmering the soy milk runs 10 to 15 minutes. Adding the coagulant and waiting for curds takes another 15 minutes. Pressing ranges from 20 minutes for a soft block to 1 to 2 hours for a very firm one.
Factory Tofu vs. Homemade
Commercial tofu follows the same fundamental steps, but at scale, consistency becomes the main challenge. Variations in the concentration of dissolved solids in soy milk can cause uneven coagulation from batch to batch, leading to blocks that differ in texture and weight. Modern factories use automated control systems to monitor soy milk concentration and coagulant addition in real time, reducing the need for workers to judge curds by eye. Automated pressing also helps standardize how much whey is removed, so manufacturers don’t have to overfill molds to guarantee a minimum block weight.
Despite the automation, the chemistry is identical to what happens in a home kitchen. Soybeans are soaked, ground, boiled, strained, coagulated, and pressed. The difference is precision and throughput, not process.