Introduction to Making Koji

Making Your Own Koji


Greetings! Welcome to the beginning of a series of followups that I’m writing in an effort to plug some of the holes in my wildly popular How to Make Sake at Home guide.

When I make a batch of sake, I normally buy some Cold Mountain Dried Koji from my local ethnic supermarket to satisfy that ingredient requirement in my recipe. I understand, however, that this product is not available in all parts of the world and therefore is sometimes impossible for hopeful sake homebrewers to get their hands on. Cold Mountain Dried Koji is a dried product, but it’s still heat sensitive and requires refrigeration, which makes mail-ordering problematic at best.

The alternative, as pointed out in the main guide, is to grow your own koji using non-perishable koji-kin (the spores of aspergillus oryzae mold) that is readily available on the supplier’s web site and from many homebrew supply stores (my LHBS stocks it). Growing your own koji from these spores is certainly economic: one 10-gram package contains enough spores to inoculate about four normal size batches (3 cups dry rice, 6 cups steamed). Also, making your own koji will allow you to take control of the quality of this single most important ingredient used in making sake.

Vision Brewing supplies instructions for using their koji-kin to grow your own koji. Following those instructions in spite of their vagueness will produce koji for you, but be aware that the amount of koji described therein is half of what you will need for a normal size batch of sake when brewing the Taylor-MadeAK way.


Making koji by hand in the traditional Japanese method.Koji is generally considered to be the most important ingredient in sake, and this is taken so seriously by traditional Japanese kura (sake breweries) that they dedicate special rooms just for growing their koji. These are nice rooms, too: paneled with nice wood, with lots of nice wooden trays to keep the incubating koji in, and temperature and humidity levels are rigorously controlled.
As homebrewers, we don’t have to dedicate an entire room to this process, but we should respect it enough to give it the personal space it requires. Besides, we wouldn’t be homebrewers if we weren’t looking for excuses cobble together new equipment to suit a task, right?

So, here’s my recommendation for equipment, inspired by dray’s topic over on the Northern Brewer board:

Incubation Equipment
Blue 28 quart Coleman cooler. A Coleman 28 quart insulated cooler. Here at the end of Summer (end of Autumn for us Alaskans, judging by all the snow on the ground), all of the coolers are on sale for pretty cheap at your local box store. I grabbed this particular model one day because I needed to transport my daughter’s ice cream cake, and it was just big enough to do the job. So, I happened to have it lying around for this project. No modifications are necessary, but it happens to be just big enough to hold….

Flat Rubbermaid TakeAlong. A one-gallon capacity, flat Rubbermaid “TakeAlong.” My wife buys these all the time for taking cookies to work in, so we always have a bunch lying around. They’re lightweight, fairly durable, flexible, dirt cheap, and come two to a pack. The lip on this vessel is just sturdy enough to hold it nice and snug in the top of the cooler while it’s full of rice, and still allows the cooler’s lid to seal. This leaves room between the bottom of the “TakeAlong” and the bottom of the cooler for some temperature management.

Heating pad inside a zip-top bag. A common heating pad. These are available in a multitude of styles and most homes just happen to have at least one lying around. Few items are better at multitasking than these devices (I often use ours to melt chocolate and incubate yogurt). Mine is folded in half and stuffed inside a gallon-size zip-top freezer bag to protect it from any condensation that forms inside the cooler. This is good to keep things warm, but you still need to have a way to keep it in check.

Brewer's Edge temperature controller. A temperature controller. If you’ve been brewing beer or making sake for a while, you probably already have one of these. The important part, in this case, is that it needs to be a model that is capable of both cooling and heating applications. The Brewer’s Edge CONTROLLER II pictured here has an internal jumper that can be moved to change it from one application to the other.

Humidity control is just as important as temperature control for making kome-koji. Referring back to dray’s example, it’s been found that covering your incubator’s sub-vessel with cellophane plastic wrap may help keep the rice from drying out while the koji grows on and into the grains. You can try the plastic wrap, but I’d rather stay away from it. You see, the aspergillus family of molds are all highly aerobic, so sealing it up air-tight with some plastic wrap probably isn’t a very good idea. Instead of the plastic, I placed a small plastic cup half-filled with filtered water on top of the heating pad. The heat evaporates enough of the water to noticeably raise the humidity in the incubator and prevents the inoculated rice from drying out. This is something that you may want to keep in mind when making your own koji.

Rice Preparation Equipment
Rice, ready for steaming. Rice steaming equipment. I’m not going to re-hash the rice steaming instructions here, but I do want to re-stress the importance of it. See, when you steam rice you’re only pushing enough water (about 30% of the rice’s dry weight) into the grain to hydrate and gelatinize the starch. This means that steamed rice, while fully gelatinized, is still very firm and pretty dry compared to simmered rice. This is important to remember because the soft grain structure and high water content of simmered rice allows the enzymes that the mold produces to reduce the rice to an unusable puddle of goo. It is for this reason that rice prepared in any other conventional cooking method is completely unsuitable for turning into kome-koji.

I don’t want to seem like I’m downplaying the importance of the rice itself, so I’ll mention that in this example I’m using the same Kokuho Rose rice that I normally use to brew my sake. You can, of course, use whatever kind of short or medium grain rice you like. If you want to resurrect the old Japanese tradition, you could even use brown rice to make your kome-koji

The smallest sieve I could find. A very small, very fine sieve. This will be used for distributing the koji-kin onto the steamed rice once it has cooled. I use this one for distributing ground spices, and I think I paid all of $1.50 for it at Wal*Mart. The all-steel construction is important for sturdiness and for ease of sanitizing. I just give it a dunk in some iodophor and shake until it’s completely dry. If you don’t have or can’t find one of these, you could follow dray’s example and double up a piece of cheesecloth around a measuring spoon and use that to distribute the spores. It’s more wasteful than the sieve because a lot of the powdery spores will inevitably get stuck in the cloth, but it’ll get the job done.

My wife's good half-sheet pan. A cleaned and sanitized aluminum half-sheet pan. Just about every home in America has some of these around. That goes double if you’re married and redoubled if you have children (mothers like to bake for their kids, right?). Aluminum, being metal, is easy to keep clean and sanitizes very well. It’s also an incredibly good conductor, which is good news when you have six cups of very hot steamed rice that you need to cool quickly without being able to add cold water to it.

Next page: Making Koji the Taylor-MadeAK Way.