Koji in the Kitchen

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Shutterstock /Brent Hofacker

In the first article in this series, we opened with a soaring overview of Aspergillus oryzae, or “koji,” covering what it is, why it works, and some of the ways it’s used. In this article, we bring it back to the home countertop and explore everyday uses for koji. You can grow it yourself, but if the process of incubating fungus doesn’t entice you, you can purchase pre-made koji and use its secondary ferments to revolutionize your cooking and preserving.

Incubation Station

If you’re ready to start growing your own koji, you’ll need to settle a few practical matters before getting started. First and foremost, you’ll need to build or assemble an incubator. Koji needs specific conditions to flourish; it prefers a hot and humid environment with adequate airflow. Koji is an aerobic mold, meaning oxygen must be available for it to colonize a substrate.

Most incubators consist of an insulated box that controls the temperature and humidity via external devices. You’ll need to keep the temperatures between 80 and 95 degrees Fahrenheit, and the humidity around 85 to 90 percent. Incubator models range from a lidded plastic container full of water with an aquarium heater, to professional-grade warming cabinets. Next, we share our personal incubator setups to help you devise your own plan.

Meredith’s Big Blue Box

“I grow koji on many things, including entire hams. As such, I needed something that would fit large, bulky items while maintaining temperature and airflow. My solution was to build a box from pieces of 2-inch foam board glued together with a food-safe epoxy. Inside the box is an incandescent heat lamp, which is plugged into an external thermostat that can be programmed to the desired temperature. For humidity, a small ultrasonic cool-mist humidifier sits in a bowl at the bottom of the box. The food destined for koji is placed in a tamis (a type of flat-bottomed sieve), covered with a flour sack towel. The tamis is supported by wooden dowels that poke through the foam board on either side. It’s that simple. As with any incubator, it has its idiosyncrasies; humidity tends to build quickly, and in great quantities. Over a roughly 48-hour incubation period of koji, I let the humidifier operate at top capacity, and then I open the incubator lid and leave it slightly ajar for the remainder of the incubation time. As you work with your own incubator design, you’ll learn the idiosyncrasies and needs of your equipment.”

— Meredith

Photo by Kirsten K. Shockey

Kirsten’s Water Bath

“My koji projects are varied, but they generally fit in a hotel banquet pan. These pans work well for a 1/2-to-3/4-inch layer of grains or legumes, or they can be fitted with a rack for less bulky meats or vegetable charcuterie. This setup employs a picnic cooler (you can upcycle an old one) and an aquarium heater and bubbler to create a humid incubation environment. To employ this system, I fill the cooler about three-quarters full with water. The aquarium heater sits in the bottom to keep the water warm, while the bubbler circulates the water to keep the temperature even. The insulation of the cooler improves the efficiency of the system.

I find this an easy system for managing mold ferments, because the water bath enveloping the floating fermentation tray not only keeps the substrate warm in the beginning, but it also cools the growing mycelium as it begins to metabolize and create its own heat. With this system, however, I’m limited by the size of the stainless-steel or glass pan that’ll fit in the cooler. Also, while its electricity use is quite low, the water must be changed after one or two batches.”

— Kirsten

Stewarding a Fungus

Once you have your incubator, you’re ready to inoculate your first batch of grains or beans, which is where we recommend starting.

Yield: about 6 cups.


  • 3 cups polished rice
    or barley
  • 1 teaspoon rice or barley tane-koji
  • 1/4 cup flour


  1. Steam the rice or barley. You don’t want the grains to be soaking wet, because then they won’t separate. Steam them until they’re al dente and crush easily between your fingers. Allow them to cool to 80 degrees Fahrenheit on a clean tea towel, separating them as much as possible.
  2. While the grains dry, sterilize the flour by toasting it in a clean pan. Once sterilized, let it cool to room temperature. Mix the tane-koji into the cooled flour, taking care with the light spores. Don’t breathe them in. When the rice or barley is around 80 degrees, use a sieve to disperse the flour and tane-koji mixture over the grains. With gloves on, mix to cover the grains as fully as possible. Once fully coated, place the inoculated grain into your incubator, and let the magic unfold.
  3. For the first 12 to 18 hours in the incubator, keep the inoculated grain between 80 and 92 degrees as the spores begin to wake up. After this point, the koji will begin to flower, taking on its characteristic fuzziness. As this happens, it’ll start to create heat, so be careful to keep the environment below 95 degrees; anything higher will kill the koji.
  4. Koji is typically ready after 40 to 50 hours of incubation. If it starts to turn olive green, it’s entered its sporulation stage. Once koji has reached this stage, you can only use it to inoculate more grain. So, aim to harvest the koji when it’s fuzzy and white or pale yellow in color.

Note: Koji grown at a lower temperature of 80 to 85 degrees will have more protease enzymes, resulting in deeply savory flavors. This koji is better for making miso and shoyu, or for curing and marinating meats. Koji grown between 85 and 95 degrees will have more amylase enzymes. These will turn starches into sugar, giving the koji the sweeter flavor needed for amazake and sake.

Guide to Buying Koji

If you’re ready to jump into growing koji, head to GEM Cultures, which has a good selection of all the basic tane-koji. They’re sold in kits that include clear and detailed instructions.

Photo by Kirsten K. Shockey

If you’re not ready to grow your own koji, but you still want to make amazake, shio koji, or miso, you can buy koji rice or koji barley from several sources. Rhapsody Natural Foods carries red barley miso koji, amazake koji, a long-term rice miso, and a short-term rice miso. South River Miso has a delicious selection of miso, and is a good resource for organic brown rice koji from the United States.

You can still peek into the world of koji without committing to full project mode. Numerous producers sell unpasteurized shio koji and amazake. Check your area for any local sellers. Aedan ships koji, misos, shio, and amazake, as well as a farmhouse sake kit.

Working with Koji

You can use your fresh koji rice or koji barley immediately, or refrigerate it for up to 10 days. If you don’t think you’ll use it in 10 days, freeze it for up to two months. Or, you may choose to preserve the koji rice or barley to use as a flavor enhancer in your cooking. To do this, dry the koji grain in a food dehydrator at 120 degrees for about 24 hours.

You can also choose to ferment further and make shio or amazake, koji’s secondary ferments. For shio koji, mix koji-fermented grains with water and 6 percent salt, and ferment again. This creates an umami-rich sauce that’s similar to soy sauce, but much quicker to produce. Instead of imparting its own flavor, as soy sauce does, shio koji allows the food to shine, amplifying flavor notes to their highest expression.

To create amazake, or ama-koji, combine koji-fermented grains with water and additional cooked grain, and then ferment again at higher temperatures, from 80 degrees for sour flavors, and up to 138 for sweeter flavors. This produces a sweeter or sour secondary ferment, as opposed to shio koji’s salty profile. Amazake is the key to making sake, and, when fermented further, rice vinegar.

Sweet vs. Salty

Amazake enhances the subtle flavors and the sweetness of vegetables. The salt in shio koji brings out the savory notes in vegetables. You can buy amazake and shio koji, but they must be raw and unpasteurized for the enzymes to do their work.

Despite their opposing flavors, these sauces are able to lend themselves to the same delicious project: koji pickles. A few teaspoons of either can transform your favorite vegetable, and draw out and intensify its unique flavors.

When choosing vegetables for koji pickles, let your imagination go wild. We haven’t yet found a vegetable whose flavor didn’t soar after a koji treatment. If you’re hesitant to make a full batch, start by testing with a small amount, or create a pickled vegetable medley, trying a bit of everything at once. Some good starters are cucumber, broccoli, Brussels sprouts (cut in half), cauliflower, turnips, carrots, green beans, squash, and melon slices.

To start, place the vegetables in a bowl and cover them with the amazake or shio koji. Make sure you fully coat the surface of the cut vegetables. Allow the vegetables to marinate in the sauce until you achieve the desired flavor. The thinner you cut the vegetables, the sooner they’ll be finished, and the more deeply the flavors will penetrate. You can let these pickles sit for as little as an hour, or as much as a full day. In general, a few hours to overnight is the perfect time frame. Taste the pickles often while you’re getting the hang of it — you’ll discover your sweet spot.

Getty Images/kuppa_rock

Another method is to place the vegetables in a re-sealable plastic bag, and spoon in a few teaspoons of the koji sauce of your choice. Seal the bag, removing as much air as possible, and move the vegetables around a bit to completely coat their surfaces.

Using koji in your kitchen is entirely possible, and always brings about enjoyable results. Luckily, there are many ways to incorporate this humble fungus into your daily diet, and every day, koji enthusiasts and experimenters find new value to lead Aspergillus oryzae into the future.

Incorporate Koji into your cooking with these recipes:

In the next article in the series, we’ll share where koji might go from here. We’ll take you deeper into working with primary and secondary ferments of Aspergillus oryzae by digging into nontraditional projects. We’ll also investigate the different strains of koji, the science of how they’re suited to different substrates, and why it matters. Lastly, we’ll talk about how the use of koji can help build a more sustainable food system, and the broader implications of the koji renaissance.

Meredith Leigh and Kirsten K. Shockey are fermentation fanatics. Their expertise spans fermented fruits, beans, vegetables, and meats. They’ve teamed up to spread the gospel of funk and the magic of koji whenever possible. Kirsten’s books include Fermented Vegetables. Meredith is the author of The Ethical Meat Handbook.

  • Updated on Aug 20, 2021
  • Originally Published on Nov 19, 2019
Tagged with: buying koji, cooking, koji, mold
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