Legend has it that during the Three Kingdoms period, after Liu Bei borrowed soldiers from Soochow, he led troops to attack Xichuan, leaving Guan Yu to guard Jingzhou. This summer, the weather was very hot, and the soldiers practiced martial arts in the sun, all sweating. After a long time, many soldiers have internal fire, dry stool, red and yellow urine, dry mouth and rotten tongue. Guan Yu was in a hurry. One day, Guan Yu was alone in his study. It was late in the morning when his men brought food, including a pickled soybean. He immediately thought of tofu. The medical book says that plaster is cool and can dispel fire. You might as well try it. Guan Yu told the sergeant to soak beans, boil pulp and order plasters himself. Because gypsum is light and tofu is tender, it can't be fried. Soldiers can only eat with salt. Coincidentally, this kind of tofu is like a good medicine. After eating, the soldier slowly got better. Later, some soldiers of Jiangling nationality mixed preserved eggs from their hometown with tender tofu and added seasonings, which not only tasted delicious, but also cleared away heat and toxic materials and became a famous dish.