The main classification method is based on the fermentation process. (Alternatively, it can be distinguished by salt-free, low-salt, high-salt, solid-liquid, warm-fermentation, and digestion methods.) This classification uses the most common industry practice.
Low-salt solid-state fermentation: Compared to high-salt liquid-state fermentation, low-salt solid-state fermentation uses a relatively low salt content, adding a larger proportion of bran, some rice husks, and a small amount of wheat flour to form a non-flowing solid mash. Fermentation is carried out by sealing the fermentation tank with coarse salt, and it matures after approximately 21 days of insulated fermentation. Soy sauce is extracted by either transferring the mash to another tank and then leaching it in the original tank.
Characteristics: Short fermentation time, strong soy sauce aroma, deep color, and lower amino acid conversion rate.
Pouring process: Fermentation is carried out in a fermentation tank with a false bottom. The liquid below the false bottom is the filtered sauce. The sauce from below the false bottom is pumped onto the surface of the mash and poured over it to achieve uniform fermentation. This is an improved process for low-salt solid-state soy sauce. It's discussed separately because it increasingly shows a trend of replacing traditional low-salt solid-state soy sauce, and its advantages-higher raw material utilization, better flavor, and lower investment in modification-have made it widely accepted by many producers.
High-salt liquid-state process: This is a fermentation process using soybean meal and wheat as raw materials, involving raw material processing, high-pressure steaming of soybean meal, roasting of wheat, mixed fermentation, and pressing to extract juice.
