Koji

Koji is steamed rice or other grain (mainly rice or barley) on which koji mold (kojikin) has been propagated. It plays an indispensable role in making sake and many other fermented foods. In sake brewing, the koji used is rice koji, made by growing yellow koji mold (Aspergillus oryzae) on steamed rice, and the enzymes produced during this process are essential. The components of koji include saccharifying enzymes such as amylase, which converts the starch in rice into glucose, and enzymes that break down rice protein into amino acids. The sugars and amino acids obtained from the rice in this way support fermentation of the shubo (yeast starter) and the moromi (fermentation mash), and give sake its characteristic flavor and aroma. In sake production, it is common for about 20% of the total polished rice used to be made into koji, and the quality and condition of the koji greatly affect the taste and aroma of the sake. As the saying "First koji, second shubo, third moromi" indicates, good koji comes first in making good sake, which is why kurabito (brewery workers) place great importance on managing the koji and monitoring its growth.