Soy sauce is also graded. According to national standards, soy sauce is also graded according to amino acid nitrogen and total nitrogen. According to national standards, soy sauce is divided into first, second and third grades according to amino acid nitrogen, total nitrogen and soluble salt-free solids. In the process of soy sauce brewing, protein in raw materials is gradually decomposed into amino acids and other components by protease, and amino acids are the basic structural unit of protein and the main nutrients of human body, especially some amino acids that cannot be synthesized by human body, which must be ingested through food. It is generally believed that the higher the amino acid content in soy sauce, the better the protein decomposition and the fresher the taste. Amino acid nitrogen in soy sauce is nitrogen in the form of amino acid, and its content is proportional to the content of amino acid. The higher the content of amino acid nitrogen, the higher the amino acid content and the higher the nutritional components. According to the content of amino acid nitrogen, the classification criteria are as follows: primary: amino acid nitrogen ≥0.7g/ 100ml secondary: 0.7g/ 100ml amino acid nitrogen ≥0.55g/ 100ml tertiary: 0.55g. Look at the quality indicators and look at the colors; Good soy sauce will foam a lot when it is shaken, and it is not easy to disperse; You can also smell it on the bottle mouth. Good soy sauce often has a strong sauce flavor and tastes delicious. The inferior soy sauce has only a small amount of foam when shaken, and it is easy to disperse. It smells like caramel and tastes bitter. Many consumers like to judge the quality of soy sauce according to its price when shopping, but it is not entirely true. Experts believe that high-quality soy sauce is clear, no precipitation, no floating film, reddish brown in color, relatively thick, lasting in hanging cups, and smells like sauce and ester. At present, there are premium, first-class, second-class and third-class soy sauce on the market, and the country also has clear regulations that the quality grade and amino acid content must be marked on the outer packaging of soy sauce. Some consumers often ignore this point when buying soy sauce, and pursue soy sauce with exquisite packaging and high price, which is not worth the candle.