How is tofu made?

1. Tofu is made from soybeans. They grow in fuzzy pods on a leafy plant. When the pods dry out, the beans inside are small, hard and yellow.
2. First the hard beans are soaked in water overnight. They soak up water and swell to about twice their size, which makes them soft enough to grind.
3. Next the soft beans are ground up with fresh water. The grinder smashes them into a thick, creamy mush called slurry.
4. The slurry is boiled, which makes it safe and takes away the raw bean taste. Then it is poured through a cloth. Smooth soy milk runs through and the pulp stays behind.
5. A little mineral salt, called a coagulant, is stirred into the hot soy milk. The protein clumps into soft white curds, leaving a clear yellowish liquid called whey.
6. The curds are scooped into a cloth-lined box with holes. A weight presses down, water drains out, and the curds join into one block. More pressing makes firmer tofu.

Step through the tofu workshop. Each step changes the beans a little more.

• 1. Soak the beans. Dry soybeans are covered with water and left overnight. They swell to about double their size and turn soft.
• 2. Grind with water. The soaked beans are ground with fresh water into a thick, creamy slurry.
• 3. Cook the slurry. The slurry is boiled for several minutes. Cooking makes soy safe to eat and removes the raw, beany taste.
• 4. Strain out the pulp. The cooked slurry is poured through a cloth. Soy milk runs through, and the bean pulp, called okara, stays behind.
• 5. Curdle the soy milk. A coagulant is stirred gently into the hot soy milk. The protein clumps into white curds that float in clear, yellowish whey.
• 6. Press the curds. The curds are scooped into a cloth-lined box with holes and pressed under a weight. Water drains away and the curds join into a block.

Add the coagulant to the hot soy milk and watch curds form. Then put weights on the press, one at a time. What happens to the block?

Experiment: What happens to the block of curds when you add more weight to the press?

1. Tap the coagulant cup and watch the soy milk curdle.
2. Tap one weight to put it on the press. Watch the holes at the bottom.
3. Add the other weights. Tap the block to see how much it wobbles.

What we found: Each weight squeezes more water out through the holes. The block gets thinner, firmer and less wobbly. That is the difference between soft tofu and extra firm tofu.

Turn on JavaScript to try it yourself.

Three cooks want different tofu: soft, extra firm and firm. Press each block to its dotted line, then serve it.

A dry soybean is a tightly packed seed. It holds a lot of protein, some oil and tough fiber. To make tofu, you have to get the protein out of the bean and into water. That is what the first steps are for. Soaking softens the bean. Grinding smashes it open. Cooking makes it safe and tasty. Straining takes out the fiber. What is left is soy milk: water full of tiny bits of protein and oil.

In soy milk the bits of protein push each other away, a little like magnets held the wrong way round. So they stay spread out and the milk stays runny. A coagulant changes that. It is a mineral salt, and when it is stirred in, the proteins stop pushing apart. They stick together in soft white clumps called curds. The clear, yellowish liquid left over is called whey.

Fresh curds are full of water, like a soaked sponge. They are scooped into a box lined with cloth, and a weight is set on top. Water drains out through the holes and the curds squash together into one block. A little pressing gives soft tofu. A lot of pressing gives firm tofu that you can slice and fry.

People have made tofu this way for about two thousand years, first in China. The sponge comparison helps with pressing, but it is not perfect: a squeezed sponge springs back and soaks up water again, while pressed curds join together and stay firm.

Key words

Soy milk

The smooth liquid made by grinding soaked soybeans with water, cooking and straining.

Okara

The bean pulp, mostly fiber, left in the cloth when soy milk is strained.

Coagulant

Something that makes a liquid clump into curds. For tofu it is a mineral salt.

Curds

The soft white clumps of protein that form when soy milk or milk curdles.

Whey

The thin liquid left over when curds form.

Protein

A body-building part of food. Soybeans have a lot of it.

Check your thinking

1. Which food is tofu made from?

   Show the answer

   Soybeans. Soybeans are turned into soy milk, and soy milk is turned into tofu.

2. You want extra firm tofu instead of soft tofu. What should you change?

   Show the answer

   Press the curds harder or for longer. More pressing squeezes out more water, and tofu with less water is firmer.

3. Why are the dry beans soaked before they are ground?

   Show the answer

   Soaking makes them soft, so they grind into fine bits. Dry soybeans are very hard. After a night in water they are soft and swollen, and they grind up smoothly.

4. What does the coagulant do to hot soy milk?

   Show the answer

   It makes the protein clump into curds. The mineral salt makes the bits of protein stick together into white curds, leaving thin whey.

5. A maker presses two batches made from the same curds. Batch A is pressed lightly, batch B heavily. How do the blocks compare?

   Show the answer

   B is smaller and firmer, with the same amount of protein. Pressing removes water, not protein. The same solids end up in a smaller block with a lower water content, which is firmer.

6. When soy milk is strained through a cloth, what stays behind in the cloth?

   Show the answer

   The bean pulp, called okara. The cloth lets the liquid soy milk through and holds back the bits of bean fiber.