« The Rice Vinegar ExperimentAkaisake - The Red Sake »

Making Koji for Homebrewing Sake - The Taylor-MadeAK Way

10/17/08

Permalink 09:05:26 pm by Bob Taylor, Categories: Homebrewing, Sake , Tags: homebrew, homebrewing, koji, koji-kin, kome-koji, sake, tane-koji

Making Koji the Taylor-MadeAK Way

I'm going to break this up into steps to help simplify a process that might otherwise seem a little complicated or mysterious. There are really only four steps, though, and most of the work is in just trying to maintain the right kind of environment for the koji to thrive in. The aspergillus oryzae strain of mold seems to do best in the 85ºF-100ºF (29.4ºC-37.7ºC) temperature range, so that's where you want to try and keep it. Whatever you do, however, don't let the temperature rise above 113ºF (45ºC) or all your efforts will result in dead mold at best (the wrong kind of living mold at worst).

What's more is that I've also learned that temperature has a definite impact on the kind of enzymes koji produces. In the lower half of koji's preferred temperature range (85ºF-92ºF [29.4ºC-33.3ºC]) the mold produces mostly protease enzymes - a property that miso and shoyu makers take advantage of to break down their soybeans. However, in the upper half of that range (93ºF-100ºF [33.8ºC-37.7ºC]), mostly alpha amylase is produced. Alpha amylase breaks starches down into simple sugars, which in turn are fermentable by yeast, so this is a property we sake brewers definitely want to take advantage of. Our target incubation temperature for koji is 96ºF (35.5ºC).

Due to its importance, the above target temperature will be often repeated in this guide.

Step 1: Assemble Your Equipment

This is the time to get all your ducks lined up. Once you start this, you're going to want to be around pretty much non-stop for the next 48 hours. This isn't something to start right before you leave for that fishing or hunting trip!

Start by assembling your incubator. Place the heating pad on the bottom of the insulated cooler, run the cord out and over the side of the cooler, and plug it into your temperature controller. Wrap the temperature controller's probe in some cellophane (secured with tape or a rubber band) to make the cleanup in your future a little easier. Place the Rubbermaid container in the top of the cooler so that it rests on the small lip that runs around the inside edge. Finally, unplug your temperature controller from its power source and do whatever the instruction manual directs you to do in order to change it from cooling to heating mode, then plug it back in and set the set point for 90ºF (32ºC) for now (the power indicator light should come on).

Start by warming up the incubator and making sure it works the way you want it to. Set the heating pad's switch on its medium setting and move the temperature controller's probe to the inside of the Rubbermaid container, then seal the cooler with its lid. The lights on the temperature controller and the heating pad should immediately come on. Keep an eye on the temperature over the next hour or two and adjust the set point as necessary to keep the probed temperature in the desired 95º-100ºF (29.5º-37.8ºC) range. Remember, the optimum temperature we're shooting for here is 96ºF (35.5ºC).

Properly soaked rice will increase in volume by 33%.

While you're waiting, wash three cups (3.5 cups or more if you want to have extra koji left over to adjust the flavor profile of your finished sake) of rice until the water runs clear, then prepare for steaming as usual by soaking in cold water overnight. Use the rest of the night to fine-tune your koji incubator.

Making koji is more technique than recipe, but it helps to know how much material you need for a batch anyway. There are only three ingredients here, and their amounts look like this:

3.50 c     Rice
1.50 ts    Koji-kin (aspergillus oryzae spores)
0.50 ts    Bleached all-purpose flour

Using this ratio, you can easily tailor the amounts according to your needs.

Step 2: Steam and Inoculate the Rice.

About 12 hours after you started soaking the rice, it will be ready to steam. I have a real abhorrence for repeating myself, so again I'm going to the original guide if you find that you need help with steaming your rice. It might be a good idea, however, to get your other tools laid out and the required one-and-a-half teaspoons of koji-kin pre-measured into the sifter while the rice is still steaming.

I've mentioned it in passing before, but I feel that this is important enough to go into detail about: in order to properly steam rice for koji or sake making, the rice needs to first soak long enough to absorb 33% of its dry weight in water. The good news for us homebrewers is that the rice will also increase in volume by the same amount. So, for small amounts like the 3.5 cups I'm using in this example, you can soak the rice in a large measuring cup and look for the expected increase in volume to know when the rice is ready for steaming: 3.5 cups of dry rice will swell to just over 4.5 cups when it has absorbed the right amount of water.

I'll update the rice-steaming instructions with this information later, but I timed this particular batch of rice while watching for the aforementioned volume increase: It took just over one hour. That's for regular old Kokuho Rose rice, not some fancy highly polished sake rice. Soaking another batch of rice overnight didn't produce a noticeable increase in volume, but it did result in steamed rice that stuck to my hands tenaciously, where the batch soaked for only an hour did not. So, there you have it: rice being prepared for steaming only needs to be soaked for an hour to absorb the necessary water, not overnight.

Hot rice!

When the long steaming is done, the rice will have again increased in volume to double the dry volume you started with. Immediately turn the rice out onto the aforementioned sheet pan (if you're smart, you'll chill the pan in the fridge first) and be careful about it! That rice is going to be very hot at first, so trying to spread it out with your hands is probably not a very good idea. A common butter knife makes a handy tool for breaking up the rice and getting it spread out until it's cool enough to handle with your hands. It won't take long to cool, don't worry. As it cools, use your clean hands to mix the rice around so that the hottest parts come into contact with the metal of the pan, breaking up clumps as you go (and fanning with a paper plate or some other device to speed the cooling, if you wish).

Once the rice has become cool to the touch, it's time to inoculate it with the koji-kin spores. Spread the rice out in a thin, even layer. Measure out the required amount of spores (1.5 teaspoons in this example - yes, I know this is three times the amount recommended in Vision's instructions, but there's a good reason for this), then measure out one third of that amount of bleached all-purpose flour and mix the two together thoroughly - this will make it a bit easier to control koji-kin distribution.

CAUTION! This is a very small amount of flour, but even so flour cannot be considered sterile and could possibly harbor contaminants that might cause your batch of koji to fail. Using bleached all-purpose flour and keeping the amount used small reduces - but does not eliminate! - the risk of failure, but the only way to be sure would be to use spores straight out of the package and not cut them with flour at all.


Put the spore and flour mixture in your sifter of choice and then use it to evenly distribute about a third of the mixture very evenly over the rice. Then put the sifter down and mix the rice thoroughly with your hands to distribute those spores. Repeat with the other half of the spore and flour mixture, followed by thoroughly mixing again, breaking up any clumps that you find with your fingers.

Health Concerns: unlike other strains of the aspergillus family, aspergillus oryzae does not produce mycotoxins and is not pathogenic like some of the more dangerous members of its genus. Still, it never hurts to be cautious. If you live with or regularly interact with individuals who have immune deficiencies, it's probably better to play it safe and not handle koji-kin around them to avoid any risk of aspergillosis.

Inoculated rice in my incubation sub-vessel of choice.

Once the koji-kin is all thoroughly incorporated, move the mound of rice to your incubation sub-vessel. That would be the Rubbermaid TakeAlong that I described earlier in the article. Spread it out evenly and move it to the pre-heated insulated cooler (henceforth: incubator). Bury the end of your temperature controller's probe in the center of the rice and seal the whole thing up.

Step 3: Koji Likes the Tropics.

Ah, a nice balmy temperature to keep our moldy rice happy.

For the next 40 to 48 hours, your only tasks are to keep the temperature and humidity in the right range and to stir the rice up every 10 hours so that the aspergillus oryzae fibers don't form the kome-koji into one big mat and to cool the culture down - more on that later. Yes, if you want to do this right you're probably going to find yourself mixing stinky moldy rice up at three o'clock in the morning. Traditional Japanese sake kura who still make their koji by hand do exactly that, and so can you. It's your option, but I suggest staying up, setting a timer, or planning ahead very thoroughly as the best options for going about this.

Use your hands to mix the rice up, but make sure to wash them well before and after. Hand washing: it's not just for the bathroom any more! Clean hands are important for growing a culture of just aspergillus oryzae (aka a monoculture) and for keeping the mold out of other parts of your home.

When you go to mix it up after 10 hours have gone by, you probably won't see any mold growth. You'll most certainly be able to smell it, however. The instructions that came with my koji-kin (and other online sources for information) talks about how koji smells "cheese-like" and "like chestnuts," but it doesn't say a darn thing about this sulfur that's being produced at the very beginning! Phew! Observe:

Inoculated rice after 10 hours.

The same can be said when you stir it up at the 20 hour mark: you might see flecks of white here and there, but not much in the way of evident mold growth. You'll know something is happening, though, because you'll get a face full of rotten eggs when you open that incubator! Here we are at 20 hours:

Inoculated rice after 20 hours.

At around the 30 hour mark the sulfur smell begins to give way to a nutty/cheesy aroma and extensive spread of the white fungus across the rice grains has become much more visibly evident:

Koji after 30 hours.

White is an important color here. If you see other colors at any time during this process, you're growing something that isn't koji, and that means you need to chuck it out and start over. At 40 hours, your koji will probably look something like this:

Koji after 40 hours.

The first thing you'll notice is that cheesy/nutty aroma has become much more intense (it almost reminds me of the kind of old and oxidized hops that lambic brewers like to use, it's that kind of smell), and the sulfur has either dissipated entirely or is masked by the other scents. Every grain of rice is nearly completely covered with white mold, but not quite. Therefore this needs some more incubation time, so back into the incubator it goes. When stirring the rice up, you might notice that it's formed into a big mat that requires a bit of effort on your part to break up - this is normal and part of the reason why the culture needs to be mixed up with your hands every few hours.

Within the next 8 to 10 hours the growing koji will really begin to generate its own heat, so monitoring the temperature and removing the culture for cooling any time it reaches 100ºF (37.7ºC) (in danger of dying) is very important. Keep a close eye on things and really observe the rice any time you take it out to cool it down. By the way, this is also the point where you will see koji really trying to bind together in one big mat. Sometime in the next few hours your koji will look something like this:

Koji after 48 hours.

Every rice kernel is almost completely covered in the white mold and the whole culture has a powerful aroma reminiscent of certain types of aged cheeses. If you taste a few grains the flavor should be nutty, slightly fuzzy, and very sweet with the cheesy notes only present as an aftertaste. This is finished koji.

Step 4: Storing it for later use.

It's time to consider your options for storage.

Here the true beauty of using a container like a flat Rubbermaid TakeAlong as a sub-vessel inside the incubator starts to show. Simply take the lid that came with that Rubbermaid TakeAlong and seal the container of koji with it.

If you plan to make sake right away, then just store the koji in the refrigerator as you use it. Sealed in its container, koji can be counted on to remain usable for at least three weeks if kept in the coldest part of your fridge.

If you don't plan to make sake right away, store the sealed container in the freezer until you're ready to use it. I've found that koji frozen in this manner can be used right out of the freezer, just invert the container and shake to loosen the frozen rice up, then break it up the rest of the way with your fingers before measuring out the amount you need. If kept tightly sealed, frozen koji should remain viable for up to three months.

Finally, for longer term storage, it is necessary to dehydrate the koji before freezing it. Spread the koji out in a thin layer (one kernel deep, if you can manage it) on a sheet pan with raised sides on it in a cool area (important!) and arrange a fan to blow cool air across it in such a way as to not blow koji rice off of the pan. Allow to dry in this fashion until the rice kernels feel hard when squeezed - about six to eight hours should do it. Once thoroughly dried, move the koji to an airtight container and store in the freezer for up to six months.

Salient Points

Let's recap the most important points that need to be kept in mind when making your own koji:

  • Properly soaked rice prior to steaming will increase its volume by 33%. Steamed rice will double its volume compared to dry rice. Even when kept in a humid environment, the rice dries somewhat during incubation and I've seen the volume shrink by as much as 12% (0.5 cup in my 6.5 cup batch, in case I miscalculated the percentage). Plan ahead with this in mind to end up with the necessary amount of finished koji for your batch of sake (6 cups in my recipe). When in doubt, make more than you think you need.

  • Environment control is very important critical to this process. Keeping the culture above 85ºF (29.4ºC) and preventing the rice from drying out will result in fast mold growth. Plan ahead and construct an incubator.

  • Incubation temperature impacts the kind of enzymes koji produces. The mold tends to produce mostly protease at temperatures between 85ºF (29.4ºC) and 92ºF (33.3ºC). That's useful for producing koji destined for making miso or shoyu, but not for sake. Temperatures between 93ºF (33.8ºC) and 100ºF (37.7ºC) seem to trigger alpha amylase production, so a sake brewer's target temperature during koji incubation is usually 96ºF (35.5ºC).

  • Beware! Koji will die if it is allowed to exceed 104ºF (40ºC) for too long!

  • Kome-koji is always white. If you're growing something that isn't white or slightly off-white, it's not koji and should be discarded and definitely not consumed. (There is an exception to this that I will go into shortly.)

  • Finished kome-koji smells powerfully like aged cheese and sweet chestnuts. Tasting some should yield obvious sweetness with nutty overtones, while the cheese-like notes will only be present as a very faint aftertaste. It'll also feel pretty fuzzy in your mouth, which should be expected because it is a fuzzy mold after all.

  • Don't let time be the sole determining factor when judging the readiness of your koji. This is something that needs more judging by the senses (sight, smell, touch, taste) and less judging by the clock.

As long as you are mindful of these points, I'm sure you will be able to grow good koji for every batch of sake, miso, and soy sauce that you want to make.

Next page: A little something extra...

Pages: 1· 2· 3