Professor Harushi Nakajima conducts cutting-edge genetic research on microorganisms, including koji fungus (also known as koji mold). In this installment, he explains the relationship between koji fungus and umami, one of the five basic tastes alongside sweetness and saltiness. He also discusses the essential role of mold in cheese—just like with koji fungus—as well as how mold is involved in the production of traditional Chinese alcoholic beverages such as huangjiu and Shaoxing wine.
Expert Commentator: Harushi Nakajima, Professor, Meiji University
Interview & text: Kenji Inoue / Photography: Koichi Mitsui / Composition: Contentsbrain / English Translation: LIBER
Japan has been a leader in fermentation technology, especially in food applications such as the use of koji fungus (also known as koji mold). Over 100 years ago, the concept of umami—now recognized as the fifth basic taste⋆1—was first proposed by a Japanese scientist. Later, the discovery of umami receptors on the tongue led to its global recognition, and umami has since become a universal term.
⋆1 Basic tastes: The fundamental taste categories that make up the flavor of food. For a long time, there were thought to be only four—sweet, salty, sour, and bitter. However, in 1908, Dr. Kikunae Ikeda, a professor at Tokyo Imperial University, identified a distinct taste in monosodium glutamate (MSG) that could not be explained by these four. He proposed the existence of a fifth basic taste, umami. In 2002, taste receptors specific to umami were discovered, and it was officially recognized as a basic taste.
The flavor known as umami is primarily associated with monosodium glutamate (MSG), an amino acid seasoning produced by microorganisms through fermentation technology. Japan was also the first in the world to successfully produce other amino acids—such as arginine and cysteine—through fermentation. This achievement is considered one of Japan’s top ten inventions of the 20th century. Driving these breakthroughs is the field of agricultural chemistry, which is our area of expertise.
Professor Harushi Nakajima, a leading expert in applied research on microorganisms such as koji fungus.
Research on koji fungus has not advanced much outside of Japan. One reason is that Europe and the United States generally lack the warm, humid climate found in Japan, so mold doesn’t grow as readily. Because mold is less familiar in everyday life, it’s often viewed primarily as a harmful organism that causes infections and disease. As a result, the idea of “domesticating” mold hasn’t taken root, making it more difficult for koji fungus research to progress in those regions.
Of course, foods made with mold also exist in the West—cheese being one of the most well-known examples. Cheese was originally developed as a way to preserve milk, a highly nutritious food, in an age before refrigeration. By introducing mold to cheese, people have been able to create a wide variety of flavors and aromas.
For example, the blue mold used in blue cheese is carefully selected to ensure it does not produce mycotoxins. When added during the cheesemaking process, it generates enzymes that break down proteins, helping the cheese to mature and enhance its flavor. Since mold cannot thrive without oxygen, the cheese is repeatedly pierced with thick needles to create air channels and ensure proper aeration.
Blue cheese made with blue mold
The mold used in Camembert cheese is a white mold. Like the blue mold in blue cheese, it does not produce mycotoxins and helps the cheese mature while enhancing its flavor. Unlike blue cheese, however, white mold is sprinkled onto the surface of the finished cheese. As the aging process progresses, the interior becomes soft and creamy.
Camembert cheese made with white mold
In Japan’s neighboring China, Rhizopus mold is used to brew Shaoxing wine⋆2. At breweries in Shaoxing City, Zhejiang Province, raw grains are ground into powder, mixed with a small amount of water, then kneaded into dumpling- or brick-shaped blocks and placed in underground chambers. Rhizopus quickly begins to grow, and eventually, yeast develops in the center, starting the alcoholic fermentation process. The resulting mash, now containing alcohol, is pressed to produce traditional huangjiu such as Shaoxing wine. The leftover mash is used as pig feed, making it an environmentally sustainable process.
⋆2 Shaoxing wine: A type of Chinese brewed alcohol made using Rhizopus mold. These brews are broadly known as huangjiu (a type of Chinese rice wine), but only those produced in Shaoxing City, Zhejiang Province, can be called Shaoxing wine.
I once tried cultivating Rhizopus mold in my lab, and it grew incredibly fast. Within just three days, the entire surface of a 9 cm petri dish was covered in long, dense mold—so much so that it even pushed up the plastic lid.
Ceramic jars filled with Shaoxing wine
Japan stretches from north to south, offering a wide range of climates and distinct seasons. Thanks to this diversity, it’s a treasure trove of fermented foods by global standards, with many regions boasting their own local specialties. I love to travel, and one of the true pleasures of travel for me is tasting these regional fermented foods—and looking forward to encountering ones I’ve never tried before.
PROFILE: Harushi Nakajima
Laboratory of Microbial Ecology, Department of Agricultural Chemistry, School of Agriculture, Meiji University
Ph.D. in Agricultural Science from the Graduate School of Agricultural and Life Sciences, the University of Tokyo. After serving as a research associate at Tokyo Institute of Technology and associate professor at the Graduate School of Agricultural and Life Sciences, the University of Tokyo, he became associate professor at Meiji University’s School of Agriculture and has held his current position as professor since 2007. Following research on baker’s yeast and organic solvent-tolerant bacteria, he now focuses on hydrophobins—proteins produced by koji fungus. He is also active in promoting education in genetic engineering, contributing to food safety policy, and supporting the International Biology Olympiad. A fermentation enthusiast, he favors barley shochu among the many types of honkaku shochu.