Even if you've never heard of koji, you've put it in your mouth in one form or another. "Koji" refers to any grain that has been inoculated with the mold Aspergillus oryzae, although it can, confusingly, also refer to the mold itself. In Japanese, the mold spores are referred to more specifically as koji-kin—a distinction we'll stick to in this post for clarity's sake. Grains inoculated with koji-kin can produce a range of flavors and products with which you're likely very familiar, from slightly sweet sake to nutty miso to intensely savory soy sauce.
But there are other uses for koji beyond making soy sauce and sake. When mixed with salt and water and allowed to ferment for about 10 days, it creates a porridge-like slurry called shio koji, which can be used as a marinade, pickling medium, or dressing. When soy sauce is used instead of salt, the mixture is called shoyu koji. Both shio and shoyu koji impart a sweet-salty dimension to the foods they're cooked with, similar in kind, if not in intensity, to miso- and sake-based marinades for meats and fish.
Koji can be made from almost any grain, so, while traditional Japanese preparations usually involved mold-inoculated white rice, barley, and soybeans, chefs across the globe have been experimenting with making other types of koji and, in turn, using those unorthodox kojis to produce oddball new misos. (David Chang, of Momofuku fame, produces what are basically miso and soy sauce analogues, which he's branded hozon and bonji, by combining basmati rice koji with nuts, seeds, and legumes.)
If you spend any amount of time looking up koji on the internet, you're likely to run across the name Rich Shih, or "Jean Dough," Shih's nom de cuisine. Shih, a mechanical engineer by day, runs the website OurCookQuest and maintains a robust social media presence, all in the service of spreading the word about a variety of food preparation methods that he views as underappreciated or misunderstood, many of which involve fermentation. (While his current obsession is koji, he has in the past focused on pursuits like making kombucha and kimchi.)
Though he lacks formal training in cooking, Shih has established himself as something of a koji authority, in part because of a seemingly relentless drive to experiment with the mold—creating koji from a range of unusual grains, including emmer and teff—and using it for novel purposes, like dry-aging meats. He's also collaborated with a number of chefs to help demystify koji and its myriad uses, projects that have come about only because he rarely hesitates to reach out to people. "I've never been afraid to ask people questions," Shih says.
I spoke to Shih to pick his brain about all things koji.
Name: Rich Shih
Day job: Mechanical engineer
How did you first become interested in fermentation?
My parents are both Taiwanese, and fermented foods were a staple in our house, so, in terms of the flavors, pretty much since I was born. My mom is a solid cook, and she'd always prepare delicious meals powered by flavor-packed preserves. What I really love is congee, a common Taiwanese breakfast. It's a simple rice porridge, served with a selection of small dishes that always includes fermented delights. I have a few favorites: an omelette with scallions and finely diced suan cai (fermented mustard greens); doufuru (spicy fermented bean curd, also known as soy cheese); and zha cai, a Sichuan spicy, crunchy pickle.
I first became interested in fermentation as a project four years ago, when I was crazy-obsessed with fish sauce. I was putting it on and in everything to unleash the umami power. I even used it to cure bacon. So good!
At the peak of my interest, I decided that I needed to know how to make it. I happened to find a chef, Geoff Lukas, who posted online about a successful homemade garum, so I reached out. He invited me into his kitchen, offered a tasting of the fish sauce, and walked me through the process. It tasted wonderful, better than any store-bought bottle I'd ever had. As part of the tasting, Geoff showed me a variety of ferments he was working on that opened my eyes to the possibilities. Of all the wonderful ferments I tasted, the one that stuck with me was the celery kimchi. The flavor and texture was amazing, and something I hadn't seen anyone else do at the time. This experience planted the seed.
What are some of the challenges you've encountered with fermentation?
There are a couple that come to mind. The first is the general public's lack of familiarity with fermented food processes in general. Most folks get nervous when you talk about using bacteria, and especially mold, to make something delicious. Many still aren't aware that the key to making soy sauce is Aspergillus oryzae. That being said, fermented flavors are increasingly popular, and more people are interested in fermenting at home. I've found that sometimes all it takes is getting someone to taste fermented flavors in a dish, and that leads to a desire to be educated and, ultimately, to acceptance.
The other challenge is established food safety regulations that don't make sense when it comes to fermented foods. The rules are overly conservative and stem from a lack of understanding. It's funny to me that our ancestors preserved foods in order to survive long before these regulations came about, and now those methods are designated illegal in restaurant kitchens. I'm hoping the resurgence of fermented foods will grow to a point that it will lead to policy changes that make more sense and make it easier for producers to provide their tasty creations to the public.
In general, fermenting requires yeast and bacterial activity at room temperature to create the flavors we love. Unfortunately, there's a rule [in restaurants] to keep prepared food refrigerated to regulate the microorganisms associated with foodborne illness. That rule does not consider environmental stages created by fermentation processes that inherently keep the food safe when prepared appropriately. The only way fermented-food producers can sell and serve their products is by going through an independent review and approval of their processes.
What is koji?
Most commonly, "koji" refers to a grain or soybean that has a specific mold, Aspergillus oryzae, grown on it. The importance of this microbe is that it consumes starch to produce enzymes to create the base of a few well-known fermented products. For sake, the mold is grown on rice to create amylase enzymes, which convert starch to sugar for alcohol production. For soy sauce and miso, the mold is grown on grains or soybeans to create protease enzymes, which convert proteins into amino acids, which we taste as umami flavor.
There are three traditional categories of miso: miso made from rice koji, miso made from barley koji, and miso made from soybean koji. For miso made with rice and barley, the respective kojis are mixed with salt and soybeans, and the mixture is allowed to ferment. Soy-only miso is a fermented mixture made up of just soybean koji and salt. Soy sauce is made by inoculating a blend of soybeans and wheat with Aspergillus oryzae, then fermenting that blend in a brine.
Polished rice is the go-to medium for koji because it's the easiest for the mold to consume when prepared appropriately. Other grains are more difficult to use due to two main factors: bran and moisture. On grains with the bran intact, the natural protective coating provided by the bran makes it difficult for the mold to penetrate. Grains other than polished rice tend to have a sticky and wet surface after cooking that is less than ideal for the mold to grow on. However, koji made with alternative grains definitely has its advantages, like vastly different flavor profiles. For example, teff koji tastes like mushrooms.
How did you get into koji? What was your first exposure to it?
I first got into koji when Geoff asked me to figure out how to make it for a brunch hosted by Sandor Katz in 2014. The theme was "fermented foods of the world," so it only made sense to include koji. I had no clue what was involved. I ended up finding a fellow named Branden Byers. He wrote The Everyday Fermentation Handbook, which includes instructions for how to make koji. I reached out to him, and he was generous enough to share all the details on how to do it, and, with his precise instructions and guidance, it was much easier than I thought it would be. I'm not sure what Geoff ended up using the koji for; I think he may have deep-fried it and used it as a garnish for some dish.
So how do you make koji?
To make rice koji, you rinse rice until the water runs clear, then let it soak for about 12 hours. You then cook the rice, but you do not prepare it as you would for eating. The grain must be al dente, for lack of a better term, to create a favorable environment for the mold to grow. You want to cook the rice enough that the mold can access the gelatinized starches, but not so much that it gets sticky. The structural integrity of the grain is also key because it creates air gaps, giving the mold more surface area to on which to grow without depriving it of access to oxygen. You wait until the rice has cooled to 110°F (43°C), then mix the mold starter in thoroughly. You then basically let it incubate at 86°F (30°C) for 48 hours. For a more detailed look at a basic technique, you can check out my friend Branden's blog post on how to make koji. It's what I used when I first started a few years ago, and it's a great basic recipe.
But this is mold we're talking about—how do you know what you've grown isn't bad mold?
It's a very specific mold that proliferates, and it looks like snow on the top. If it's bad mold, you can kind of smell a difference. If you're making koji and it's good, it's very sweet-smelling and aromatic. Some people describe it as having a slight grapefruit smell. I think David Chang at some point said it smelled like Fruity Pebbles. If it goes bad, it smells like green bananas, and that's more from bacterial spoilage than from another mold.
You have a very sanitary environment that you've only inoculated with this one mold, and you're cultivating it under conditions in which only that mold will survive. I've never had a problem with other things coming up. The only time I've had issues is when I've tried a new grain that's hard for koji-kin to grow on.
How much koji do you make at a time?
I make the koji in two-inch hotel pans in my incubator, and each tray yields four pounds. I can get two trays into my incubation chamber. I usually get, like, eight or nine pounds a run. For fresh koji at room temperature, you want to use it within the day you make it. It's fine refrigerated for about a week, but if you want to keep it longer than that, you can freeze it, and it keeps for a pretty long time, about six months to a year. You can also dry it. I've never dried it—as with preserving or keeping anything, you lose freshness, and I imagine you also lose some enzyme activity when you dry koji. When you buy dried koji in the store, it's not as good as fresh at all—there's no comparison.
What is it about koji that you find so compelling as a subject for experimentation?
Its versatility and reach are truly amazing. In terms of creating umami/amino acids, it's the closest to alchemy that cooking can get. I've found that you can make practically any protein more delicious. You can follow the process of making soy sauce and miso with any protein base you desire. Koji can be applied to whole pieces of meat or fish with the shio koji technique as well. Koji's enzymatic power also accelerates the drying of charcuterie, on the order of one-third less time. The application of koji to dairy creates a complex, Parmesan-like flavor in a couple months, instead of a year. For starches, it's great to create sweetness and umami in grains, breads, and pastries, and it works as a driver for secondary ferments, like kombucha, sourdough, et cetera. It's also used in a pickling method called bettarazuke that's pretty great. In short, koji is magical. The only limit is your experience and imagination.
When did you decide to start devoting a significant amount of time to making koji?
I can't say there was a specific decision made. I was intrigued by every part of koji- and miso-making from the beginning. There was, and still is, so much potential to realize. Once I started, I went crazy sharing what I was doing with as many food folks as would listen via blog posts, social media, workshops, and visiting chefs in their kitchens. It's important to me that anyone who is creating food has the opportunity to work with this special ingredient.
A significant moment I recall happened two years ago: Two chefs, Jeremy Kean [chef and co-owner of Boston's Brassica Kitchen] and Patrick Soucy, on separate occasions, tasted a sampling of what I was working on. Independently, they each wanted 20 pounds of koji to work with in a week. This triggered the need to scale up from the experimental-batch quantities I'd been making. Once the koji was ready, we met in their kitchens and created a wide variety of miso flavors. We created unique umami sauces that wouldn't have happened otherwise. The most interesting things I recall from all the experimentation was Jeremy's hazelnut whey miso and Patrick's mussel fish sauce. This interaction is just one of the many exchanges I had with folks to help plant the seeds of koji-powered food-making. We started a community.
Do you think working with koji has made you a better or more curious cook generally?
Nah. Since I started cooking, I've always been curious, investigating and experimenting to expand my knowledge every day. I typically discover a subject of interest and dive in to understand everything I can. I just happen to be down the koji rabbit hole at this point in time.
What's your favorite food preparation (to eat) that incorporates koji?
I can't say that I have a favorite. I can say that I am in love with adding koji to dairy to create a complex flavor profile in a relatively short period of time. A few years ago, I was testing miso with alternative bases beyond what I had seen. One day, I decided to swap out cooked soybeans for ricotta cheese. After two months of fermentation, I squeezed it out and dried it into a hard cheese, which I then grated on everything. After that, I added yogurt and koji to hot sauces, which gave the hot sauces an incredible umami backbone. I also found that protein-packed whey powder can be converted into a delicious processed-cheese sauce.
What's your favorite food preparation to make using koji?
No favorites. I really like bettarazuke, a Japanese-style pickle that is made with koji, cooked rice, sake, and salt. This pickling process is the result of combining a series of fermentation processes. The rice koji produces enzymes to convert starch into sugar. Then naturally occurring yeast and bacteria in the air, as well as on the vegetables, power lacto-fermentation (as in kimchi) and vinegar production for multidimensional souring. Traditionally, the pickle is made with daikon or eggplant. I like using beets and sunchokes. The flavor is a great harmony of sweet, sour, salty, and umami, and it's got a nice crunch.
Is there a recipe you've come up with that you're particularly proud of? What about it is important to you?
I recently made a blueberry koji kombucha fruit topping, matched with a buttermilk umami ice cream on a smoked coconut waffle, that I really loved. It's important to me because it's a harmonized composition of multiple layers of fermented flavors, built on ideas I developed from the ground up. Traditionally, when you make kombucha, you use tea and sugar water. In this case, I used black tea and the sugar produced by jasmine rice koji in place of cane sugar. I then mixed the finished koji kombucha, which was slightly sweet and vinegary, with fresh blueberries and reduced the mixture to make a fruit sauce. The umami hit in the buttermilk ice cream was made by fermenting buttermilk, sweetened condensed milk, koji, and salt into a sweet-and-savory "soy sauce." It added a blue cheese note to the ice cream that made it sing.
Do you have kitchen tools that you can't live without?
An incubator is a must for making koji. The mold requires a very specific environment to grow. That being said, it's straightforward and inexpensive to create the appropriate conditions. I have detailed blog posts on a couple methods—like using an immersion circulator to create small batches of koji and using a cooler rig for larger batches—that will get you there.
Any tips for anyone looking to fool around with koji at home? Ideas about where to start?
Any resources in particular you'd like to highlight?
- The Book of Miso, by William Shurtleff and Akiko Aoyagi, has everything you need to get started with miso-making. It is all-encompassing, with recipes, science, history, charts listing every type of miso, et cetera. It was published way ahead of its time. Unfortunately, it's out of print, but readily available on Google Books; used copies are also inexpensive. One of my silly side goals is to bring it back into publication.
- Gem Cultures is the best US-based source I've found to buy Aspergillus oryzae spores. They have a wide selection to make any type of koji your heart desires.
- The Nordic Food Lab blog has several wonderful in-depth posts on koji and their innovative applications.
- #kojibuildscommunity on Instagram is where folks of all experience levels are sharing their koji-based makes, experiments, and questions.
- #opensourcegastronomy on Instagram is a place where chefs and experienced cooks are sharing a wide range of culinary ideas that includes the subject of koji.
You speak frequently about building a community of people brought together by koji. What is the end goal of that community? A koji incubator in every house?
Koji is just the beginning. The core focus is to share knowledge, ideas, and methods for food preparation, and to inspire others to do the same.
A few years from now, we hope to have a food education center where folks of all backgrounds (chefs, cooks, scientists, historians, artisans, artists, engineers, tradespeople, et cetera) can come to teach, learn, and innovate. Our space will welcome anyone who is interested, no matter what their experience level. At the very least, there will be a communal kitchen, farm, preservation/fermentation building, and maker space.
Can you tell us a little bit about the products we've photographed?
For the popcorn koji, I popped the corn with no seasoning, misted it with water until moist, dusted it with amylose flour (Hi-Maize resistant starch), mixed in the koji-kin, and incubated it under the same conditions I would for koji (86°F/30°C at high humidity) for 48 hours. I chose popcorn to optimize the conditions for the mold to grow. Its low density and high surface area make it easier for the aspergillus to infiltrate. Popcorn also has a multitude of air pockets between the pieces when piled together. I used amylose powder because I had past successes with making koji faster with jasmine rice, which has a high amylose content for rice. Making that connection, I did research to find amylose in a concentrated form. I discovered Hi-Maize resistant starch, which is produced as a filler for commercial baked goods. When I fed it to koji-kin, it grew like crazy.
I made the Aspergillus oryzae–inoculated cheese using a fairly standard process, with the spores added to the cooled milk. After I separated the curds and pressed them, I incubated the cheese under favorable koji conditions. After that, I aged it in my refrigerator. All based on a patent I read.
I made the charcuterie—wild curry bresaola, wild curry beef tongue, and Cajun guanciale—by following standard salt-curing preparations. The bresaola and beef tongue were seasoned with a wild curry spice mix from my forager friend, Mallory O'Donnell. Upon completion of the curing stage, and just before drying, I mixed fresh koji with 3% salt into a paste and applied it to the exterior of the meat. (You can read more about it on my blog).
The sweetfish roe amino paste/sauce experiment is based on my past successes with using the miso fermentation method to create umami pastes with everything from bacon to cookie dough. I use a 1:1 ratio of any protein paste to koji, plus 5% by weight salt against the total. Then you wait... (Here's a post on the same method, but using dairy as the base.)
This interview has been edited and condensed for clarity.
Editor's Note: Welcome back to Obsessed, the interview series in which we talk to uniquely driven amateurs and professionals from all across the food world. We hope to shed light on the passions that inspire enthusiastic food nerds, from home cooks to chefs on the line to veteran butchers, fishmongers, and farmers. Hopefully we'll also pick up some of their favorite tips, tricks, and food wisdom along the way. Know somebody who you think would be perfect for this interview series? Email us!