OK, so what exactly are we trying to do when making koji? Well, to examine this we need to consider the role koji plays in Sake Brewing. In sake brewing we use koji to provide a wide variety of products. These include products that provide flavor and aroma elements as well as enzymes which degrade proteins and starches into smaller component parts. For example proteins are disassembled into peptides and amino acids while starches are converted into smaller starches, dextrins and sugars.
Rice starts out with 7% to 8% protein, but much of this is milled away, so we do not focus on koji’s production of enzymes to break down this protein. Rice starch is our main focus and needs to be broken down as effectively as possible into sugars. Koji produces alpha, beta and gama amylase. Depending on how we culture the koji, we can emphasize protein or starch degrading enzymes. High temperature cultivation, 98°F to 110°F, lead to the production of saccharification enzymes whereas lower temperature cultivation, from 98°F down to 68°F, emphasizes protein degrading enzymes. So to make good koji for sake brewing we must culture the koji at high temperatures.