We welcome Dr. Takeo Koizumi, a leading authority in fermentation studies. Thanks in large part to his efforts, “Washoku: Traditional Dietary Cultures of the Japanese” was inscribed on UNESCO’s Intangible Cultural Heritage list in December 2013, followed by Japan’s traditional sake-making using koji fungus⋆¹in December 2024. But what exactly is “fermentation”? Dr. Koizumi explains the relationship between fermentation and Japanese food culture, along with the unique characteristics of fermented foods.
⋆¹ Sake-making using koji fungus: Japan’s traditional sake-making using koji fungus (also known as koji mold) was inscribed on UNESCO’s Intangible Cultural Heritage list as “Traditional Skills and Knowledge of Sake-making with Koji Mold in Japan.”
⇒Read Part 2: “Japan’s Food and Sake Cultures Owe Much to the Blessings of Koji Fungus.”
Expert Commentator: Takeo Koizumi, Professor Emeritus, Tokyo University of Agriculture
Interview & text: Chieko Fujita / Photography: Koichi Mitsui / Composition: Contentsbrain / English Translation: LIBER
Japan:The World's Leading Fermentation Powerhouse
Japan is the world’s number one fermentation powerhouse. There are around 90 types of pickled daikon alone, and across the country, roughly 2,000 kinds of pickles exist. In Europe, when you think of pickles, sauerkraut and gherkins might come to mind, but beyond that, there aren’t many well-known varieties.
Japan, on the other hand, is blessed with the perfect conditions for fermentation—both in terms of climate and geography—and is home to a wealth of high-performing microorganisms. Each sake brewery, as well as miso and soy sauce producers, often have their own unique strains of yeast or lactic acid bacteria that have evolved and been preserved over time. For nearly 2,000 years, the Japanese people have been eating foods created through the work of these microorganisms. This long history and deep connection with fermentation make Japan’s fermentation culture truly remarkable. I believe it’s something we should share more widely with the world.
Japanese Cuisine Wouldn’t Exist Without Fermentation
Have you heard of Washoku⋆², Japan’s traditional food culture that has been recognized by UNESCO as an Intangible Cultural Heritage? At its core is the simple meal style known as ichiju-issai—one soup and one side dish.
This ichiju-issai style consists of just rice, miso soup, and a side dish—but two of these are fermented foods: the miso in the soup, and pickles as the side dish. Without fermented foods, Japanese cuisine simply wouldn’t exist. Imagine sashimi without soy sauce—it would feel incomplete. Simmered dishes in Japanese cuisine rely on mirin, and vinegared dishes use rice vinegar. And of course, traditional Japanese alcoholic beverages like honkaku shochu（single-distillation shochu） and sake are also made through fermentation. In short, fermentation is essential to Japanese food culture.
An example of ichiju-issai: rice, miso soup with tofu and fried tofu, and pickles
⋆² Washoku: A traditional food culture cultivated within Japan’s climate and natural environment. In December 2013, “Washoku: Traditional Dietary Cultures of the Japanese, notably for the celebration of New Year” was inscribed on UNESCO’s list of Intangible Cultural Heritage.
Takeo Koizumi, Professor Emeritus at Tokyo University of Agriculture
Fermenting Food Promotes Maturation and Helps Prevent Spoilage
Fermented foods have the following five key characteristics.
The first is that fermentation makes food less likely to spoil. This is a truly fascinating phenomenon. The difference between fermentation and rotting lies in their usefulness to humans: fermentation benefits us, while rotting does not. Rotting belongs to the realm of death and disease, whereas fermentation creates things that support human life.
For example, if you pour milk into a bowl and leave it out overnight in the middle of summer, it will spoil—and drinking it could cause food poisoning. That’s rot. But if you add lactic acid bacteria instead, the milk turns into yogurt, which is much less likely to spoil. That’s fermentation. It naturally preserves and protects the food.
Fermented foods resist spoilage because the microbes and yeasts that drive fermentation produce natural antibiotic substances that prevent harmful bacteria from invading. In other words, they establish a stronghold and grow to sufficient numbers to crowd out rival bacteria. As a result, food that goes through fermentation matures but does not rot.
Fermentation Boosts Nutritional Value—Fermented Foods Are the Ultimate Natural Foods
The second key characteristic of fermented foods is that fermentation significantly enhances their nutritional value. For example, if you compare raw soybeans to natto⋆³—which is made by fermenting soybeans with Bacillus subtilis var. natto—there’s a roughly 130-fold increase in stamina-boosting amino acids. On top of that, fermentation makes the food far more flavorful. Why does it taste better? Because the proteins in the soybeans are broken down by the power of fermentation microbes into amino acids, which are the source of both umami and energy.
⋆³ Natto: A quintessential Japanese fermented food made by adding Bacillus subtilis var. natto to steamed soybeans. It is known for its strong smell and sticky, stringy texture.
Fermentation also increases the vitamin content of food. It boosts peptides as well. In short, fermentation multiplies the number of compounds that are beneficial to the human body. What really sets fermented foods apart from ordinary foods is this: they contain living microorganisms—fermentation microbes—that enter your body when you eat them. That’s what makes fermented foods fundamentally different from other types of food. In a sense, they are living foods.
For example, just one spoonful of yogurt introduces hundreds of millions of living lactic acid bacteria into your body. The microbial cells themselves enter in large numbers. That’s a feature rarely found in foods other than fermented ones.
The third key characteristic of fermented foods is that their smell and taste become completely different from the original ingredients. Milk and cheese taste nothing alike. The same goes for soybeans and natto. People often associate fermentation with strong or unusual aromas, but that’s not always the case. Sourdough starter, for example, has a pleasant smell. And among Japanese sake brewed from rice and rice koji , certain types like ginjo-shu have a fruity aroma. Fermentation also dramatically enhances umami flavor.
The fourth characteristic is that fermented foods are the ultimate natural foods. They contain no additives, yet are rich in umami and keep well, so they can be eaten just as they are.
The fifth feature is their cultural and historical depth. This aspect runs incredibly deep. Across different regions, there are traditional fermented foods with long and storied histories. That’s why I’ve made it my mission to share these remarkable facts about fermentation with as many people as possible.
⇒Read Part 2: “Japan’s Food and Sake Cultures Owe Much to the Blessings of Koji Fungus”
PROFILE: Takeo Koizumi
Born in 1943 into a sake-brewing family in Fukushima Prefecture, Takeo Koizumi is Professor Emeritus at Tokyo University of Agriculture and holds a doctorate in agriculture. He is a fermentation scholar, food culture expert, and author. His areas of specialization include food culture, fermentation science, and brewing studies. He has also served as a visiting professor at Kagoshima University, Fukushima University, Beppu University, Ishikawa Prefectural University, and Miyagi University, among others. Dr. Koizumi has authored more than 150 books on fermentation. He has held numerous roles, including Chair of the National Fermentation Town-Building Network Council and member of The Washoku Association of Japan. In December 2024, he served as the lead of the initiative that successfully registered “Traditional Skills and Knowledge of Sake-making with Koji Mold in Japan” as a UNESCO Intangible Cultural Heritage. Through a wide range of food-related activities, he continues to share the wonders of fermentation both in Japan and abroad.