What You Need to Know
Proteases from Aspergillus and endogenous soybean enzymes hydrolyze proteins into peptides and free amino acids, producing umami glutamates and flavor‑contributing compounds such as 5′‑methylthio‑2‑methylbutanal and 2‑methylbutanal. Amylases from the mold break down starches into simple sugars, which are further metabolized by lactic acid bacteria, lowering the pH to 4.5–5.5 and contributing to the characteristic tang of miso. Optimal aging at 15–20 °C maximizes flavor development; temperatures above 30 °C accelerate spoilage and generate off‑flavors such as sulfurous or rancid notes.
The Science
Primary Reaction
Fermentation of soybeans by Aspergillus oryzae and lactic acid bacteria, involving proteolysis, amylolysis, and acidification.