The following 101 on koji rice comes from HOMEGROWN member and ace fermenter Todd. Thanks so much, Todd, and please keep the good ideas cooking!
Hello! Todd Van Horne here, and I’ll be teaching you about koji rice: what it is, how to make your own, and how to use it once you’ve made it.
My wife and I run a small café in Wakayama, Japan, called Hatsugaya. We grow our own rice—actually, her mother does most of the work—and we serve it as sprouted brown rice in our restaurant. The word “sprout” in Japanese is “hatsuga,” and “ya” is a common suffix for a shop name, hence the name of our restaurant. (Well, to be precise, the character we use for “ya” is not the common character meaning “shop” but instead the character for “house,” which is a cute play on words and reflects our vision for our restaurant. Just to get technical about it.)
I picked up fermenting as a hobby a few years ago and recently got into koji. I’m not a health nut. I just love to make things and am fascinated by the power of living foods, which we can harness and use but can’t own or control.
When you think of fermented foods, you’re likely thinking of lacto-fermented foods, in which specific bacteria flourish and digest sugar. Lacto-fermented foods include things such as sauerkraut, yogurt, bread dough starter, and the like. Koji is something different entirely.
Koji is a mold. The next obvious question is: Why would you make your rice moldy on purpose? Koji is a specific strain of mold that has been cultured over the centuries. Its very special property is that it digests starches and proteins into sugars and amino acids. Koji is the first step in making sake, soy sauce, and miso, which I bet you’ve eaten. So now that you know you’ve already ingested it, it’s not so scary, is it?
On that note, I’ve seen some health-oriented websites in English steering people who are worried about food allergies away from koji because it is a mold. Rest easy: I’ve never once heard allergy concerns about koji in Japan, and food allergies are just as prevalent here as they are in other countries. Actually, koji breaks down many allergens, so Japanese people with wheat allergies don’t worry about soy sauce, for example. That said, if you’re celiac, please don’t run out and try this, but do be aware that there are more facets to multicultural foods than show up in their host cultures.
Once you’ve got koji, what can you do with it? You can try making sake, which is actually quite easy in its simpler forms. You can make a miso, or a living pickling base. But the easiest first project is shio-koji, or salt koji, which is enjoying a huge resurgence in popularity as a versatile seasoning. (More on salt koji and how to make it later on.) Remember those amino acids that koji makes? Those are the natural base for umami, or richness—one of the five basic tastes. You’ll find that even a small amount of salt koji really brings out the flavor in most dishes. But first we’ll cover how to make koji rice. Let’s get started!
WHAT YOU’LL NEED
» uncooked white or brown rice* (A minimum of 1 1/2 kg, or about 3 1/3 lbs, is a good batch size for first timers. You need a critical mass of rice to build up some heat for fermentation; using too little could lead to failure. I recommend white rice for your first few tries.)
» koji starter, called koji-kin mold seed: 2g per kg of rice** (or, using the batch size above, about ¾ tsp for 3 1/3 lbs rice)
» cheesecloth or very clean T-shirt (launder, soak in vinegar water, and air dry)
» probe thermometer
» food-safe plastic bag
» Styrofoam box, cooler, or similar insulated container
» low heat source, such as an electric blanket, hot water bottle, or low-watt light bulb
» alcohol or peroxide in a spray bottle for disinfecting
*A note on brown rice: White rice is brown rice that has had the hull removed. The hull of brown rice is impenetrable to the koji mold, so I run my rice through a huller at one of the lowest settings, checking that the hull is either partially removed or at least scratched. If you are using store-bought brown rice, you can accomplish this to a certain extent by massaging the rice really hard when you mix in the koji-kin seed mold, but you still could end up with a failed batch. I recommend starting with white rice to get the hang of the process; then, if brown rice turns out to be difficult, you’ll have a better idea how to troubleshoot.
**You can find this online. Homebrew shops (fairly likely) and Asian markets (less likely) also may carry it.
1. Wash your rice. If you are using white rice, wash and rinse until the rinse water no longer runs white. If you are using brown rice, this should be quicker; just make sure all of the dust has been washed away.
2. Soak the rice. White rice should be soaked for 12 hours if it’s warm, 24 hours if it’s cold. I recommend sprouting brown rice for 2 to 3 days, changing the water as needed. Otherwise, soak as white rice.
3. Drain. Let the rice sit in a colander for at least an hour, shaking occasionally. If water remains between the grains of rice, the rice will cook instead of steam and will end up too soft for good koji rice.
4. Steam the rice. Line your steamer with cheesecloth. Put the rice in and wrap it up a bit. Get your water to a full boil before setting the steamer on the base pot. The goal is to get the core of the rice soft without overcooking it. White rice will take about 45 minutes; brown rice will take about 50 minutes; brown rice soaked for 2 to 3 days will take about 30 minutes. Remove and check a grain or two before the full time has elapsed to make sure you’re not overcooking your rice. When you can push your fingernail through the grain, or when the core of the grain doesn’t feel different from the rest of the grain, your rice is done cooking. If you don’t have a steamer, there are many ways to improvise one, but I strongly caution against boiling rice directly in water!
5. Empty the rice into a shallow tray, and cool by turning with a spoon or spatula and fanning. If you have a Japanese fan, you can be very traditional, but I use an electric fan as it’s faster and easier to control. (If I fan by hand, then my spoon hand wants to fan, too, and rice ends up everywhere—that old pat-your-head-rub-your-belly conundrum.)
6. When the rice reaches 40 degrees C (104 degrees F), or just slightly warm to the touch, add your koji-kin. There are a number of things to be careful of here. The mold is incredibly fine, so disperse it as close to the surface of the rice as you can. Also disperse it as evenly as you can across the surface of the rice. Most people use a strainer of some sort to separate the mold seeds from the seed rice grains that they’re grown on, but I just cut a small hole in the seed bag and shake the koji-kin and the seed rice out together. The seed rice grains will turn black by the end, so you can pick them out if you want. The benefit to this method is that there is quite a concentration of koji-kin on the seed rice grains, so those can work in your favor. Most professionals are probably proud of how much koji they can make with a minimal amount of koji-kin. If you do this often, you can start to reduce the amount you use, but 2g of starter per kilogram of rice is a good amount for beginners, as you won’t fail for lack of koji-kin.
7. Spread the koji-kin evenly throughout the rice by massaging it in with your hands. It’s best to put a little elbow grease into the massage, since scratches and breaks in the grains will help the mold seat. If you’re using brown rice, this step is especially important. By this point, you should be working quickly to prevent the rice from cooling too much. Meanwhile, set up your low heat source in your insulated container.
8. Wrap your rice back in the damp cheesecloth, aiming for as close to a sphere shape as you can; put it in a plastic bag; and set it in your insulated container. You want to maintain the temperature in the container between 30 and 35 degrees C (86 to 95 degrees F). If you have a fancy temperature controller, 33C (91F) is good. Use a spray bottle to dampen the inside of your container and maintain high humidity. From now on, we’ll be counting by hours, so this is your zero hour.
9. Leave the ball for about 20 hours, checking its internal temperature periodically. As the mold starts to grow, it will produce heat. If your ball doesn’t rise above the ambient temperature within 20 hours, something went wrong and you should start over. More likely, the ball will be in danger of overheating. If it reaches 42C (108F), remove it, mix it around until it’s 32C (90F) or so, and put it back. I try to keep mine under 40C (104F); more on that later. Check the humidity level when you open the container. If it’s low, spray again.
10. At around 20 to 22 hours, your rice should be heating up quickly, even if you remove it to cool it down. After sterilizing your hands, mix the rice well to get uniform heat throughout the mass. Spread the rice evenly in a tray no more than 1 1/2 inches deep, cover it with your dampened cheesecloth, and return it to your heated container. At this point, I lower my container temperature to 29C (84F). Continue spraying to maintain high humidity in your container.
11. From this point through the end of the process, you want to monitor the rice’s temperature and remove it from the heater if the temp exceeds 42C (108F). If the temperature climbs too high, you can mix it to cool it, but you want to avoid this if you can. Around hour 30, you’ll notice that the mold is spreading quickly and forming a solid mass. This is called matting. After this happens, one method of cooling the rice without mixing too much is to break off large chunks of the mat and flip them over, like pancakes. This will allow the bottom side of the mat to cool and may help regulate the rice’s temperature.
12. From hour 38 or so on, I stop spraying and crack the cooler lid to allow the humidity to drop. This apparently signals the mold that it should be flowering soon and encourages the deepest mold penetration into the rice grain.
13. The 48-hour mark is a good time to stop the fermentation, although you can allow the koji to continue forming through 55 or even 60 hours—but if you notice some areas turning yellow, finish it immediately. The color change means the mold is about to flower and the flavor of the koji will be compromised.
14. You can put your finished koji in a baggie and refrigerate it for a few days, freeze it for a month, or spread it out to dry and then freeze it for longer storage. Of course, the fresher the better!
A note on temperature control and mixing. There seem to be two camps: the people who mix to reduce temperature and the people who don’t mix after the first mixing at hour 20. The latter group gets very matted, fluffy white koji. The former group may get better penetration into the rice grain. I’m still experimenting, but the instructions above follow the first approach. If you want really fluffy koji, move the koji to a cooler area rather than mixing to control its temperature.
Your first time or two, you should be happy if you get good covering and fuzziness. Eventually, though, you may want to start fine-tuning your koji based on your intended use. One really interesting thing about koji is that between 32 and 36C (90 and 97F), it produces more amino acids as it breaks down the starches, and between 36 and 42C (97 and 108F), it produces more amylase, or sugar. Sugar is the base for the alcohol produced in sake, so for sake koji, you’ll want the higher temp range. Amino acids are the source of the umami flavor, so if you’ll be making shio-koji, miso, soy, or other food flavorings, you’ll want to aim for the lower range. All koji has sweetness and umami, so don’t worry if you’re off by a bit. You’ll still get a good koji.
One thing worth mentioning is that koji doesn’t care whether it’s day or night. I’m writing this after waking up at 4 a.m. to check on my latest batch. You can control your zero hour and fudge your checkpoints a bit so that you can check your koji at, say, midnight and 6 a.m. You’ll just need to plan your batch accordingly. As a hint, a zero hour of 9 a.m. or 10 p.m. works well.
If you followed all these steps and ended up with koji, good for you! Let’s use some of your koji right away to make shio-koji.
HOW TO MAKE SHIO-KOJI, OR SALT KOJI
WHAT YOU’LL NEED
» fresh koji
» sea salt: enough to equal 30 percent of the weight of your koji
» good water
WHAT TO DO
Mix your salt and koji, rubbing it firmly until the salt is evenly distributed. It’s OK to smash some of the koji grains.
Put the koji/salt mix in a good container (non-lead ceramic, glass, or food-safe plastic), and pour your water in until it covers the surface of the koji. Stir twice a day for 1 to 2 weeks—2 weeks in winter, 1 week in summer, as warmth speeds up the ripening process—and you’re done! You can marinade meats, make pickles, or just use your shio-koji as a salt substitute. Shio-koji is incredibly versatile and can be used in any kind of cooking.
A note on salt and water: Please do not use table salt! In fact, please never use table salt, except for chemistry experiments! Table salt is pure salt, high in sodium, and has no nutritional value other than iodine. Sea salt has a variety of trace minerals that are good for you and adds a much more complex flavor to your foods. Because of this, you should be able to use less than when using table salt. Water will also affect the flavor of your shio-koji, so use filtered water or a trustworthy bottled water (if there is such a thing). Best of luck to you! Please post comments to let me know about your successes, learning experiences, or any questions.
Got a question for Todd? Or another use for salt koji? Post it below and keep the conversation rolling. If, like Todd, you've got a penchant for fermenting, you might consider joining the HOMEGROWN group I Could Ferment That. You might also give the 101s on kimchi, kombucha, and kefir a gander, or check out those mentioned above, on sauerkraut, yogurt, and sourdough starter. You can always find more things to cook, preserve, make, craft, plant, grow, and mix in the HOMEGROWN 101 library.
ALL PHOTOS: TODD VAN HORNE