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Tofu, aka bean curd, is curdled soy milk. Tofu was invented in China around 2,000 years ago and became a daily food around the year 1300.
To make tofu, cooked soy milk is cooled to 175 degrees Fahrenheit and coagulated with calcium or magnesium salts dissolved in water. This takes anywhere from eight minutes to half an hour. When curds have formed, the remaining "whey" is ladled off, or the curd is broken up to release water and drained.
The mass that is left over is then pressed for fifteen to twenty-five minutes while still hot. The tofu is then cut into blocks, packaged in water and pasteurized.
The texture of tofu can be altered by freezing it. When tofu is frozen and then thawed, it is able to absorb cooking liquids and has a chewier, meatier texture.
One of the earliest European accounts of tofu comes from Friar Domingo Navarrete in the 17th century: "...the most usual, common and cheap sort of food all China abounds in, and which all in that empire eat, from the Emperor to the meanest Chinese; the Emperor and great men as a dainty, the common sort as necessary sustenance. It is called Teu Fu, that is a paste of kidney beans. I did not see how they made it. They drew the milk out of the kidney beans, and turning it, make great cakes of it like cheeses, as big as a large sieve, and five or six fingers thick. All the mass is as white as the very snow, to look to nothing can be finer ... Alone it is insipid, but very good dressed as I say and excellent fried in butter."
Info from:
"On Food and Cooking" by Harold McGee.
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