Making Koji – Home Brew Sake

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.

Continue reading “Koji production – what are we trying to do?”

In order to make koji for brewing sake we need to go through the same steps that we do to prepare rice for brewing sake. In fact, it is often the case that a portion of the rice goes directly into the brewing sake while another portion is used for koji. So, as always we begin by washing the rice. This is to remove all contaminates, including the powder (Nuka) that remains after milling and any material added by the miller, like iron. Removing the nuka lowers the stickiness we will have after steaming. And, as mentioned elsewhere, iron is very bad for sake as it darkens the sake and speeds a reaction of residual sugars with amino acids that harms the flavors and aromas.

Washing the rice is followed by steeping the rice until we reach the desired water uptake level, usually between 25% and 35%. If the uptake of water is too little the rice will not steam properly leaving a hard uncooked center that the koji mold will not penetrate. On the other hand having too much water uptake will cause the rice to be too mushy and sticky after steaming. This results in a base that is too easy for the koji mold to penetrate and this prevents or lowers the production of transformative enzymes we want. Most rice used for hombrew sake will need to steep between 30 minutes and two hours. As homebrewers we are more often than not more guilty of soaking too much than too little. Continue reading “Making Koji for Sake”