Koji ratio (koji buai)

Koji ratio (koji buai) is the proportion, expressed as a percentage, of rice used for making koji (koji rice) relative to the total weight of polished rice used in a single brewing batch. Specifically, it indicates how many kilograms of koji rice are used for every 100 kilograms of polished rice, and it is commonly set within a range of 20% to 30%. Because this ratio has a major influence on the flavor and aroma of the sake, it is a very important factor in sake brewing. Koji plays a key role in saccharifying (converting into sugar) the starch needed for fermentation and shapes the quality of the sake, so it calls for the experience and skill of the brewers.