Doing Fieldwork on Fermented Foods in the World

(Mar.22-Sep.24, 2022, Nagoya University Museum)

Special Display 4

Japan’s National Microbe “Koji Fungi” *

■ Is koji that Supports Asian Fermented Food Culture a Symbol of Authority?

Koji is one kind of microorganism that we Asians find indispensable to brewing and fermentation. In recent years, as you know, there has been a koji boom and a “drinkable intravenous drip, amazake” boom, with koji playing a part in fermented food booms. However, when asked what sort of thing koji is exactly and what microorganisms are used in it, I think practically nobody knows the answers.

Koji is defined as “rice, wheat, soybeans, or other grains on which microorganisms composed chiefly of Aspergillus oryzae and other mold species effective in food fermentation have been bred.” In simple terms, koji is “rice or beans with koji mold growing in them intended for use in fermented foods.”

■ The Function of Yeast in Fermented Foods…

So, what kind of abilities does koji mold have that are used in food fermentation? Simply speaking, koji mold is basically “proficient at breaking down nutrients in food.”

For example, when making liquor from rice or wheat, the base material is starch. Yeast, which performs the alcohol fermentation does not have the ability to use starch, so some way is needed to break the starch down into glucose and maltose—sugars that yeast can use. koji mold produces lots of amylase, a group of enzymes that breaks down starch, so when the Asians produce liquor from rice, they use koji to enable the yeast to perform its fermentation.

In addition, koji mold produces lots of protease enzymes , which break down proteins, and lipase enzymes, which break down fats. So when producing soy sauce or miso, koji is used to perform the function of breaking down the starches, proteins, and fats in the soy beans, wheat, and other ingredients. The use of salted koji to soften meat comes down to the utilization of the proteases koji mold produces.

■ The De-fanged Wolf “Koji Mold”—Japan’s National Microbe

Various kinds of koji are used in different parts of Asia, but in Japan, mold of the genus Aspergillus is primarily used. While mold of the Aspergillus genus is great at breaking down nutrients in food, on the flip side of the coin, it basically produces mycotoxins, so it is a “dangerous wolf,” which can be fatal to humans if ingested. None of us humans, however, are currently dropping dead from eating koji. This is because our ancestors skillfully selected genetic variants of koji mold that do not produce mycotoxins, and these have been passed down and used by succeeding generations. Maybe koji mold really is a “defanged wolf.”

Also, I think there are many people who know that Japan’s national flower is the cherry blossom, and its national bird is the pheasant, but I think few know that Japan’s “national microbe” is Aspergillus oryzaekoji mold.

The Japanese people having miso soup and rice for breakfast, enjoying an evening drink of Japanese saké and topping that off with soy-sauce ramen can give thanks today again for the blessings of their national microbe, koji mold.

* The English title has slightly been changed from the panel.