How long does it typically take to make koji?

The process of making koji typically takes about two days, which is the correct answer. During this process, steamed rice is inoculated with koji-kin (Aspergillus oryzae) spores. After inoculation, the rice is maintained in a warm and humid environment to encourage the growth of the mold.

Within this two-day period, the koji-kin grows throughout the rice, converting the starches into sugars, which are crucial for fermentation. The transformation facilitated by the koji is an essential step in sake production, as it significantly impacts the overall flavor profile and quality of the final product.

Longer periods, like three or five days, would not typically occur in traditional sake brewing practices, as the koji process is optimized for efficiency to ensure a vibrant fermentation process while maintaining quality. Therefore, the duration of two days strikes a balance between effective mold growth and prompt utilization in sake brewing.