What You Need to Know
Polished rice is steamed and inoculated with Aspergillus oryzae (koji) at 30–35 °C to enzymatically hydrolyze starches into maltose and other sugars. The resulting mash (moromi) is cooled to 15–20 °C and inoculated with Saccharomyces cerevisiae, which ferments the sugars into ethanol, CO₂, lactic acid, acetic acid, and a complex array of flavor‑contributing esters, aldehydes, and higher alcohols. Precise temperature control below 25 °C and strict hygiene prevent off‑flavors and contamination.
The Science
Primary Reaction
Starch → Maltose (α‑amylase, β‑amylase) → Ethanol + CO₂ (yeast fermentation)