Experimental, innovative, and originating from ancient Japanese culinary customs, koji coffee proves that the future of coffee may very well be in fermentation.
A fungus of staggering complexity, koji starts small—with its powerful conversion of starch to sugar occurring at the near-microscopic level—but it brings a powerful punch of flavor to the dishes it composes. While it’s no stranger on the table, forming the base of soy sauce and the briny bite of tsukemono pickles, and appears as a common feature in Japanese drinks (such as Japan’s national brewed beverage, sake) koji has primarily remained within the realm of Japanese cuisine.
However, as fermentation continues to enter the repertoire of intrepid culinary pioneers, such as Noma, the powerful mold has progressed to the international stage, and even one step further, into cups of coffee. And while the transformative power of fermentation has been a frontier dabbled in by coffee connoisseurs, from winemaking-inspired carbonic maceration to the natural process of organic fermentation occurring as coffee cherries dry, koji remains comparatively unexplored outside of select scenes.
From miso to macchiatos, this mighty mold might now be redefining what fermentation can mean, turning centuries-old koji culinary wisdom into the next wave of coffee innovation.
What is koji?
Koji is a spore synonymous with Japanese cuisine. If you’ve ever sipped on the savory broth of miso soup or dabbed a piece of sushi into a dish brimming with soy sauce, then you’ve encountered Japan’s indigenous koji mold, whether you’ve known it or not.
Typically, the koji mold starter is added on top of a grain, such as rice, soybeans, or barley, and meticulously monitored to ensure optimal fermentation standards, during which over 30 types of enzymes are produced. These include protein-busting proteases that create a deep umami flavor, and amylase, which converts starch into sugar.
The production of this gastronomic powerhouse is safeguarded by a select few family-operated koji starter companies within Japan, with techniques and intricate know-how often passed down in the family, some for 600 years or more. This helps preserve this culinary (and microbial) culture for generations to come.
How did koji and coffee get their start?
A stalwart staple on Japanese tables, it wasn’t until bioscientist Koichi Higuchi dabbled in coffee bean experimentation that the hidden potential of koji in coffee was first actualized. More than just a mere food scientist, Higuchi is also theseventh-generation descendant of an Osaka-based koji starter company, surrounded since birth by the culinary chemistry behind raising and utilizing koji. Seeking to shake up a stable industry, where the last major mold innovations came about during the cusp of modernity in Japan’s Meiji Period, Higuchi ventured to test an unconventional theory– that koji, when applied to coffee, could mimic the digestive, enzyme-producing process involved in kopi luwak.
The findings were startling—and sweet.
As research continued to progress, koji coffee became ready for its international debut, with World Barista Champion Kaapo Paavolainen unveiling a koji coffee in the Milano-based 2021 World Barista Championship. A cup born in collaboration with Higuchi, Paavolainen sought victory through the flavor-enriching profile brought about by koji. While coming short of securing the top prize, this novelty launched koji coffee into the coffeehouse spotlight.
Now, it’s a technique that’s on the upswing. While not yet commonplace amongst everyday coffee drinkers, the use of koji in coffee is growing in popularity, mirroring similar growth and interest around fermentation in the culinary world.
Coffee is of course no stranger to fermenation. The natural process involves naturally occuring fermentation that happens as coffee dries. But kofi offers a twist—or rather, a sprinkle—of an additional interaction to the mix. Similar to how koji is dashed atop a mound of steamed rice during sake’s production process, with temperature and humidity maintained to foster optimal starch to sugar conversion, koji can be dusted atop green coffee cherries during processing unlocks the force of additive fermentation. The koji bacteria then grow on top of the coffee cherry, tapping into the bean’s latent sweetness to surpass the limits of sugar content achieved using more conventional methods.
The result? A coffee capable of bringing rounder, creamier, and sweeter notes out of coffees of all types.
Modern usage of koji in coffee
Much like the venerable position of the toji, or the brew master, who oversees the production of sake at sake breweries with a piercing eye for detail and unyielding oversight to all things occurring in the fermentation process, koji-curious coffee baristas must be equal parts mad scientist and disciplinarian—daring to adventure, even audaciously so, yet strict in control and scrupulous in notating every detail of the process.
Beyond the flavor-enhancing properties, koji coffee also contains the potential to support regions conventionally thought to produce lower-quality beans, such as India or Mexico, by harnessing the existing flavors hidden within the bean. However, not all agree with the claims that koji can radically transform the existing industry, as koji spore starters themselves continue to pose a challenge as a pricey upfront cost to consider. Coffee expert and Sprudgie Award honoree Christopher Feran has written extensively about this process.
Koji coffee stands now as an innovation that invites both artisans and drinkers alike to reimagine what’s possible when ancient fermentation meets modern caffeine culture.
Conclusion
If anyone ever asked you how you’d feel about adding a little mold in your daily brew, chances might have been high that questions would be met with a resounding refusal. And yet, koji contains a promising potential to enhance whatflavor we get out of our coffee and how we get that flavor out of our coffee.
We live in an open-minded time when it comes to coffee processing, a collision of science and ingenuity and risk. Some coffee purists may sneer at the sheer idea of additive fermenting, while others see it as the next evolution in how we understand and craft flavor—an intersection of culinary science and coffee artistry. Koji, long celebrated in the worlds of miso, sake, and soy sauce, is now cementing its place in coffee, unlocking layers of sweetness, depth, and umami that traditional methods have yet to reach.
A little mold never hurt—in fact, it just might help redefine the future of coffee.
Taylor Bond is a freelance journalist based in Tokyo. Read more Taylor Bond for Sprudge.