The Art of Koji Making

First Koji, Second Moto, Third Moromi

The ancient brewing maxim ichi-koji, ni-moto, san-moromi places {{glossary:koji}} making as the single most important step in sake production. The quality and character of the koji sets the foundation for everything that follows.

Preparing the Rice

Rice destined for koji is steamed to a firm, separate-grained texture — harder and drier than rice for eating or for the moromi mash. The exterior should be dry while the interior remains moist. After steaming, the rice is cooled to approximately 35 degrees Celsius before entering the {{glossary:koji-muro}}.

Inoculation (Tane-tsuke)

The brewer sprinkles {{glossary:tane-koji}} spores over the cooled rice, then mixes thoroughly to distribute the spores evenly. The amount is tiny — roughly 100 grams per ton of rice — but the distribution must be uniform. The inoculated rice is then piled and covered to retain warmth and moisture.

The First 24 Hours

During the first day, the {{glossary:aspergillus-oryzae}} mold germinates and begins colonizing the rice surface. The brewer monitors temperature closely, periodically breaking apart clumps and redistributing the rice to ensure even mold growth and prevent hot spots.

Tsuki-haze vs Sou-haze

Two principal koji styles exist. Tsuki-haze (spot koji) shows mold concentrated in spots on the grain surface, producing primarily amylase enzymes for clean, dry sake. Sou-haze (total koji) shows complete surface coverage, producing both amylase and protease for richer, more umami-forward sake.

The Final Hours

By hour 36-48, the koji room fills with a distinctive sweet, chestnut-like aroma. The finished koji grains feel dry and firm, with visible white mold growth. The brewer assesses quality by breaking a grain open — proper koji shows mold hyphae penetrating into the {{glossary:shinpaku}} core.