Salt in China is divided into coarse salt and refined salt (refined salt) according to the processing methods, and their quality differences are as follows: (1) Particle size: coarse salt is unprocessed large-grained salt, and refined salt is processed large-grained salt, with flaky shape and small shape. (2) Salty taste: The impurities in the raw salt contain acidic salt compounds (magnesium sulfate and magnesium oxide). After hydrolysis, these acidic salt molecules will stimulate the taste nerve, so coarse salt is more salty than fine salt. (3) Aroma: When the magnesium chloride in the raw salt is heated again, it will decompose into hydrochloric acid gas, which can help protein in food to hydrolyze into delicious amino acids. Stimulating the olfactory nerve will make people feel that the taste of coarse salt is stronger than that of fine salt. (4) Sodium chloride: The main chemical component of salt is sodium chloride. Sodium chloride can help the human body penetrate. For example, after food is digested and becomes soluble, it must have sufficient concentration to penetrate into the blood through various cells, so that the nutrients in it can be sent to various tissues of the human body. So sodium chloride plays a great role. Generally, the raw salt contains 85% ~ 90% sodium chloride, and the refined salt is above 96%. (5) Soluble matter: The main chemical components of salt include water, magnesium chloride, magnesium sulfate, potassium chloride, calcium sulfate, iodine and other trace compounds in addition to sodium chloride. These compounds are essential substances for human body, and exist in a certain amount in crude salt, but they are removed in refined salt processing. From the comparison of the above two, people eat crude salt in their daily life, which is more beneficial to their health than eating refined salt.