Finding Koji: Cultivating the Backbone Of Japanese Cuisine

Koji, scientifically known as Aspergillus oryzae, is a mold that has been cultivated in Japan for centuries. It plays a fundamental role in Japanese cuisine, serving as the backbone of many essential ingredients such as miso, mirin, and rice vinegar. Beyond its use in cooking, koji is also crucial in the production of traditional Japanese beverages, including amazake, shochu, and, most notably, sake.

Recognized for its deep cultural significance, koji-based sake production was officially added to UNESCO's Intangible Cultural Heritage of Humanity list in December 2024.

To celebrate this global recognition, the Japan Sake & Shochu Information Center hosted a media gathering on February 19. It brought together experts and enthusiasts to highlight the craft and tradition behind Japan's iconic drink.

*Dr Hiroshi Konno gives examples of items made with koji. (©JAPAN Forward by Natasha Takahashi)*

Protecting the Tradition

As Japan's sake industry continues to navigate modernization and global expansion, there is a growing effort to preserve the time-honored techniques that define traditional sake brewing. This balance between innovation and heritage is at the heart of the recent UNESCO recognition. It further reinforces the importance of safeguarding Japan's brewing culture for future generations.

Shuso Imada, General Manager of the Japan Sake & Shochu Information Center, emphasizes this delicate equilibrium. "In this day and age, it is difficult not to evolve. But this tradition of sake-making must be protected," says Imada. "Being recognized by UNESCO is a great honor, and we hope to expand sake globally while keeping true to our roots."

*Dr Hiroshi Konno with an image of Aspergillus Orzyae. (©JAPAN Forward by Natasha Takahashi)*

Cultivating Koji

Although a staple in Japanese cuisine, only a handful of koji producers remain in Japan. Dr Hiroshi Konno, a renowned agricultural chemist and president of Akita Konno, a microbial starter company, describes the intricate process of making koji and the unique biochemistry behind sake production.

The process begins with preparing the starch, which serves as nutrients for the koji mold. The rice is washed, soaked, and steamed. Once cooled, the koji starter and sake yeast are combined with water, initiating the fermentation process.

*Taste testers of sake, shochu, and mirin. (©JAPAN Forward by Natasha Takahashi)*

Contrast in Methods of Fermentation Across the Globe

Wine and beer also undergo fermentation, yet sake's production is distinct. Wine undergoes only alcohol fermentation, and beer separates saccharification and alcohol fermentation into two phases, In contrast, sake allows both processes to occur simultaneously. This unique mechanism enables sake to achieve a higher alcohol concentration than wine or beer.

As Dr Konno explains, "This simultaneous saccharification and fermentation process is known as 'parallel fermentation.' In contrast, beer follows a different fermentation process, occurring in sequence."

*Amazake taste tester with radish pickled in koji. (©JAPAN Forward by Natasha Takahashi)*

Similar brewing techniques exist across Asia, but Japan is the only country that uses its native fungus, Aspergillus oryzae, in alcohol production. This is due to the cultivation process, other nations typically use a natural fermentation process that does not rely on a specific strain of fungus. Its reliance on steamed rice and high-temperature cultivation prevents unwanted microorganisms from interfering with the fermentation.

As Dr Konno puts it, "Producing alcohol using this technique is a remarkable example of Japanese technology. That is to say, sake brewing is not just about making sake — it is about developing the technology to brew sake."

Domestication of Mold

Some may still have an aversion when they hear the words "mold" or "fungus." In fact, the wild variation of Aspergillus Orzyae is highly toxic. However, through centuries of refinement, Japanese sake makers have successfully purified the mold to ensure it is safe for consumption.

"Japanese koji mold does not produce any toxins. To explain this concept, let me use an analogy with wild boars and domestic pigs. Wild strains of Aspergillus produce harmful toxins." says Dr Konno

"However, through selective cultivation over many years, Japan has domesticated koji mold in a way similar to how wild boars were domesticated into pigs. This means that the koji mold used in Japan is completely different from the toxic strains of Aspergillus found in the wild. Naturally occurring molds should not be used for brewing, as they may contain harmful toxins."

*Dr Hiroshi Konno shows the process of making koji starter. (©JAPAN Forward by Natasha Takahashi)*

Koji and Its Diverse Flavors

The intricate art of sake brewing is deeply influenced by the environment in which koji is cultivated. Factors such as humidity, temperature, and water content all play a crucial role in shaping the final flavor profile. Because of this sensitivity, no two sakes are exactly alike. Each batch also carries subtle variations that reflect the brewer's technique and the conditions in which it was made.

Dr Konno highlights this complexity:

"How you treat the koji can change everything about the sake," he says. "The various levels of water can alter the amino acid concentration. And the temperature can change the palate as well — some sake will have a sweeter profile, while others may be more sour and fragrant."

Author: Natasha Takahashi