Chemical principle of making tofu: The main ingredient of soybean milk is protein. Because of carboxyl and amino groups on the surface of protein, colloidal substances with the same charge are formed on the surface of protein particles, so that the particles repel each other and cannot sink together. After the brine is lit, because there are many electrolytes in the brine, many positive and negative ions are formed in the water, which destroys the repulsion and makes protein combine with precipitation to form tofu. Salting-out: 1. Salting-out generally refers to the process of adding inorganic salts to a solution to reduce the solubility of a substance and precipitate it. Such as: the process of condensing protein by adding concentrated (NH4)2SO4; The process of adding saturated sodium carbonate solution in the esterification of acetic acid to reduce the solubility of ethyl acetate and make its stratification phenomenon more obvious. 2. After adding some inorganic salt solutions to some protein solutions, protein can be condensed and separated from the solution, which is called salting out and can be recovered. Adding some heavy metal salts to some protein solutions can cause protein to condense and precipitate from the solution. This effect is called denaturation, and its properties change and it cannot be recovered. 3. Put animal fat or vegetable oil and sodium hydroxide in a saponification pot according to a certain proportion, stir and heat, and the higher fatty acid sodium, glycerol and water formed after the reaction form a mixture. Add salt particles into the pot, stir and stand, so that the higher fatty acid sodium is separated from glycerol and water and floats on the liquid surface.