Both edible salt and industrial salt contain the chemical composition of sodium chloride, but the processing technology of raw materials is completely different. The process of industrial salt is simple. But edible salt is different. It needs to remove some heavy metals harmful to human body, and then it can be produced through a series of steps such as crushing, washing and drying. At present, the industrial salt is between 400 and 500 yuan per ton. Generally speaking, 900 yuan of edible salt is 800 ~ 1 ton. When brewing soy sauce, 15% salt is generally used. Calculated, a ton of soy sauce with industrial salt is about 60 yuan cheaper than edible salt. Industrial salt contains a lot of sodium nitrite. Sodium nitrite is mainly used in dyes, medicine, printing and dyeing, bleaching and so on. Because of its coloring, antibacterial and antiseptic effects, it is often used as a coloring additive for cooked meat products in food industry. China's Hygienic Standard for the Use of Food Additives stipulates that the maximum dosage of sodium nitrite in meat is 0. 1.5g/kg, and its residue in meat products shall not exceed 0.03g/kg；. It shall not exceed 0.05g/kg in canned meat products.