There are different opinions about the origin of tofu, but most people think that it started with Liu An, the grandson of Liu Bang, the ancestor of the Western Han Dynasty. Liu An, known as the King of Huainan, has a mother who likes to eat soybeans. One day, her mother was ill in bed. King Huainan ordered people to grind soybeans into powder and add water to make soup for her to drink, but she was afraid that the food was tasteless, so she added some salt to taste. Unexpectedly, it actually condensed into pieces, which is the formation of the initial prototype of tofu. Because Liu An was an alchemist, when the prototype of tofu was made, he used the alchemist to do experiments. After many studies, he finally found that gypsum or salt can solidify soybean milk into tofu, which is very delicious for cooking, and tofu began to spread among the people.
There is also a story about the origin of tofu. There is a family of three, a couple and a mother live there. Unfortunately, the mother-in-law is not good to her daughter-in-law, and even won't let her drink ordinary soybean milk. One day, my mother-in-law left, and my daughter-in-law began to grind beans and cook soybean milk. But when the soybean milk was boiled and she was filled with joy, footsteps came from the yard. The daughter-in-law is afraid of being a mother-in-law. When she sees it, she will be scolded, so she quickly picks up the whole thing. It turns out that the jar was soaked in sauerkraut before, and there was some sour soup bottom in it, so the soybean milk solidified as soon as it was poured in. The young couple barely tasted it and found that the solidified soybean milk was delicious, tender and delicious, so they named him "Doufu" and tofu came from it.
It is also said that the origin of tofu can be traced back to the Han Dynasty. During the Han Dynasty, farmers in the Huaihe River valley used stone mills. Farmers soak rice and beans in water, put them in a water mill with a funnel, grind them into paste and spread them in a pot to make pancakes. Pancakes and homemade soybean milk are the daily food of farmers in two stones in Huaihe River. Farmers have accumulated various experiences in planting, boiling, grinding and eating beans. Inspired by the long-term deterioration and coagulation of soybean milk, people finally created the earliest tofu by primitive self-sedimentation.
Whether tofu started here or was created by Liu An, we should still thank our ancestors for their wisdom in the past to create this nutritious food today.
Some people divide it into two groups: North Tofu and South Tofu. The difference is roughly as follows: North tofu, also known as old tofu, is made of brine (magnesium chloride), with little water, milky white color and slightly sweet and bitter taste. It is advisable to stew for a long time, including frying, collapsing, pasting, frying and stuffing; South tofu, also known as tender tofu, is made of gypsum (calcium sulfate) and contains 90% water. It is white in color, fresh in texture and sweet and fresh in taste. Suitable for mixing, frying, stewing, boiling and soup making.
As for the third question, to be exact, it is brine, which is used to make tofu. Brine, also called bittern alkali, is the liquid that seeps out in the process of salt making. The main component of brine is magnesium oxide, followed by sodium chloride and potassium chloride, and also contains trace elements. Used to make tofu (which can solidify protein). Brine has a strong stimulating effect on skin and mucosa, and has an inhibitory effect on the central nervous system, which can be poisoned to death.
Soak soybeans in water, grind them into soybean milk, boil them, and then add bittern to the soybean milk. At this time, many glistening things are separated, and once filtered, they are made into tofu.
As for how ancient people got bittern, please refer to this post:
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Internal fat tofu is a production technology introduced from Japan in recent years, which uses grape acid internal fat instead of brine or gypsum as the coagulant of tofu. Internal fat tofu has no bitter taste of traditional tofu, and it has developed rapidly in southern coastal cities in recent years.