What You Need to Know
During the koji stage, Aspergillus oryzae secretes proteases and amylases that break down proteins into peptides and amino acids and starches into reducing sugars. In the brine, these substrates undergo the Maillard reaction, forming melanoidins and volatile sulfur compounds that give the sauce its brown color, umami flavor, and antioxidant properties. The process also lowers pH to 4.5–5.0, enhancing preservation.
The Science
Primary Reaction
Maillard reaction between amino acids and reducing sugars during fermentation