There are several theories about its discovery, none of which are supported by clear evidence. According to some sources, it was the noble Liu An who discovered tofu around 164 BC in a region of northern China; another hypothesis refers to chance, suggesting that when soybeans mixed with dirty sea salt (rich in calcium and magnesium salts) were boiling, the coagulation process was spontaneously activated, leading to the formation of curds and the subsequent coagulation of the mass.
Finally, it is believed that ancient Chinese learned the curd formation method by copying similar techniques for cow's milk from the Mongols: supporting this theory is the etymological similarity between the Mongolian term "rufu" (milk that has gone bad) and the Chinese word "doufu", which indicates curdled milk.
During the process, boiling soy milk creates a thin soy milk membrane, rich in proteins, which coagulates on the surface: this membrane is collected and dried into yellowish sheets known as tofu skin or yuba.
