Seikiku (Koji making)
Japanese: 製麹（せいきく）
The general term for the process of cultivating koji mold on grains. Temperature, humidity, and time determine quality.
Seikiku is the process of sprinkling tane-koji on steamed grains and cultivating koji mold over 40-48 hours with temperature and humidity control. Stages include inoculation, turning, portioning, and final care.
The ideal is 'so-haze' — mycelium penetrating deep into the grain — but penetration degree is adjusted by purpose. Too hot weakens enzymes; too cold prevents growth. Koji making is a dialogue with microorganisms. Brewers waking repeatedly through the night to check temperature resemble parents watching over a newborn. Sparing no effort is the only path to good koji.