What is koji anyway? Well koji is rice with a white mold covering it. The mold is Aspergillus oryzae and it is the key to sake because of the enzymes it creates. These enzymes primarily break down the starches in the rice creating sugars needed for fermentation. So how do we get koji?
Koji is available in most good sized Asian markets. While this is not the best koji for sake, it is serviceable. Then there is sake brewer’s koji. The one I carry is here. You can also make your own. To make your own you need to start with the Aspergillus oryzae spores. Tane-koji (dried koji that was let go to spore) is one source of these spores. Another is koji-kin which is a processed tane-koji to separate out the spores. Technically speaking I believe tane-koji and koji-kin are the same thing but for the products I have seen it seems to separate out as whole rice vs. powder. In any case we can use these spores to inoculate steamed rice to culture up some fresh koji.
There are only a few widely available koji-kin products outside Japan. The one I currently carry is here. These products generally come with instructions for making koji but no matter how good the instructions may be, making koji takes practice. Each of us have our own environment, pans, steamers and such which make the process just different enough that it takes experience to know how the koji will turn out in our environment. It can take making several batches of koji before you get the knack of it. For this reason, I would not recommend planning to make sake from your first batch of koji. Make it and sure, if it turns out well, use it to brew sake but don’t box yourself into a corner from the outset.
Once you have your koji, whether purchased or made, the Sake brewing process is the same for whatever type of sake you plan to make. So choose your path and get started.