The umami flavor of soy sauce depends on its amino acid nitrogen content. Generally, the higher the amino acid nitrogen content, the higher the grade of soy sauce, meaning better quality. According to my country's national standard for brewed soy sauce (GB/T 18186-2000), soy sauce is classified according to its amino acid nitrogen content as follows:
Grade 1: ≥0.80g/100ml
Grade 2: ≥0.70g/100ml
Grade 3: ≥0.55g/100ml
Grade 4: ≥0.40g/100ml
However, this does not mean that the higher the amino acid nitrogen content, the better the soy sauce. Blended soy sauces may also have high amino acid nitrogen content, or some unscrupulous suppliers may add excessive amounts of umami enhancers, resulting in high amino acid levels, but this does not necessarily indicate high-quality soy sauce.
Besides identifying quality through amino acid nitrogen content,you can also observe the color: Pour the soy sauce into a white porcelain dish and swirl it. Light soy sauce will be reddish-brown, while dark soy sauce will be brownish-brown and glossy.
Taste: Light soy sauce tastes saltier; dark soy sauce has a savory, slightly sweet flavor.
Usage: Light soy sauce is used for seasoning; due to its light color, it's often used in stir-fries or cold dishes. Dark soy sauce is generally used for coloring food, and is better suited for braised dishes and other dishes requiring color. It's suitable for braised pork, marinated foods, and cooking dark-colored dishes.
