What You Need to Know
Miso production begins with Aspergillus oryzae (koji) enzymes that hydrolyze soy protein and starch into peptides, free amino acids (especially glutamate) and simple sugars. Lactic acid bacteria and yeasts then metabolize these substrates, generating lactic acid, ethanol, esters and other volatile flavor compounds. Controlled temperature, salt concentration, and aging time drive the Maillard‑like reactions that deepen color and flavor while suppressing spoilage microbes.
The Science
Primary Reaction
Enzymatic proteolysis and saccharification of soybeans by Aspergillus oryzae followed by lactic acid fermentation and alcoholic fermentation by indigenous bacteria and yeasts