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Japanese Sake and My Life with Koji Mold



On 24th May, 2016, the fourth symposium held by the Japanese Civilization Institute took place at Japan University of Economics in Shibuya, Tokyo. Mr. Katsuhiko Kitamoto, former appraiser of the National Research Institute of Brewing (NRIB) and now research professor of Nihon Pharmaceutical University and professor emeritus at Tokyo University, presented his lecture entitled, “Japanese sake and my life with koji mold,” which is copied below with permission of the Japanese Civilization Institute.


I would like to talk about koji mold today. I’m sure everyone knows a lot about Japanese sake, but there are few who know about koji mold. What makes Japanese food different from, say French food and Chinese food is “umami (pleasant savory taste)”. Lying at the base of umami are seasonings like miso (soybean paste), soy sauce and mirin (sweet sake). What they have in common is koji, or koji-kin (koji mold). In other words, the key ingredient of umami in Japanese food is koji mold.


I have long been studying just koji mold. For 20 years, I worked at the Institute of Brewing in Takinogawa, Kita Ward. During that time, I also worked at the Regional Taxation Bureau of Fukuoka and Sendai and served as appraiser of sake. In 1995, I became professor emeritus at Tokyo University and have made a transition to studying basic biological issues ever since. My days at the Institute of Brewing, was spent on studying sake yeast and koji mold—two microbes essential for sake making.


I have also participated in the development (breeding) of sake yeast, which outcome can be seen in Kyokai Sake Yeast No. 1901—a High Ethyl Caproate Productivity that produces no Urea—distributed two years ago by the Institute of Brewing.


It goes without saying, that koji is essential for sake production. When you scratch some koji mold and put it above some nutrient agar, then look at it through a microscope, you see thin thread-like cells connected to each other like bean sprouts. These are the seed malt of koji and we also call them moyashi (bean sprouts). Recently, Japanese food is seen by the world as a healthy cuisine. Studies show how koji mold itself that is included in Japanese food has functions of health, and is slowly being developed.


Excuse me for my long introduction. Let us return to our theme and talk about how Japanese sake is made. When you look at the text books of sake production, you see the famous phrase; “Ichi: koji, ni: moto, san: zukin” (first koji, then the yeast starter, then fermentation). In other words, koji is the most important component in sake production.


The main ingredient of sake is rice. Rice is polished, washed, soaked in water and steamed to make steamed rice. 20 percent of this is then used for making koji, while 80 percent is used for preparing seed mash and moromi (mash). The seed mash is the starter. For example, when 1000 kg needs to be prepared, 7 percent or 70 kg of rice is cultivated in a clean culture as starter. The starter takes two weeks to complete. Then, it is used to prepare moromi three times. By the time moromi is completed, 18 percent of sake is produced in the  course of a month. It is then compressed and filtered and clear sake is produced.



Liquor produced by fermentation using only fermentation skills include, wine, beer and Japanese sake. Amongst them, Japanese sake takes the most complex route of brewing production, called the multiple parallel fermentation process. Wine undergoes a singular fermentation process, in which the yeast simply ferments the various saccharides, like glucose and fructose fruit sugar included in the ingredient of wine—grapes. Beer, on the other hand, converts barley starch into sugar. Using malt, sweet juice (wort) is produced from amylase contained in malt. It undergoes a preliminary saccharification step of converting starch into glucose, which is then filtered. The transparent fluid is then fermented with beer yeast. The process of fermentation and saccharification is different. It is known as a singular fermentation process.


In contrary, Japanese sake is more complex. Glucose of rice is produced from fermentation mash that remains in the tank. It undergoes a multiple parallel fermentation process, in which glucose is fermented to alcohol as soon as sake fermentation begins. While alcohol percentage is about 5 percent for beer, 10 percent for wine, an extremely high alcohol percentage of 20 percent is produced with Japanese sake due to the skilled fermentation technique. Two types of rice are used, sakamai (sake rice) and rice used for food. Sakamai is rice exclusively used for producing sake. The rice we normally eat is about 22g for a thousand grains. Yamada Nishiki sake rice is slightly bigger, about 26.6g for the same amount.


When you look closely, you see a milky white colored part in the center of the grain, which is referred to as shinpaku. Shinpaku causes reproduction of koji mold resulting in producing a fine mold. Amongst the many sakamai, Yamada Nishiki is the most famous, and is used often to make ginjo-shu (sake made from highly polished rice using special technique). Ginjo-shu labled “Yamada Nishiki 35 percent” is made of white rice polished to 35 percent, after being shaved 65 percent from the outside with a rice-polishing machine when it was brown rice. A large amount of nuka (rice bran) is extracted at this stage, which is used to make rice crackers and cosmetics. Dassai’s company produces rice flour bread from ginjo-shu in collaboration with Kobeya Baking Co., which is said to be delicious with the glutinous texture it provides.


The reason why the rice is polished is because the taste turns stale. The rice we regularly eat is white rice that is shaved 10 percent from brown rice. Brown rice is rich in nutrition be it minerals, protein or fat, but that part acts negatively for sake flavor, so it is shaved off. Generally, an average of about 30 percent of Japanese sake is shaved off from the brown rice, but ginjo-shu—that’s become popular today—shaves about a half. There is an indication standard for ginjo-shu that more than 40 percent needs to be shaved. The more it’s polished the more the starch gets purified, resulting in fine sake. From experience, it is proved that protein and fat lessens, and the fragrance of ginjo-shu is extracted and its taste becomes more delicate when this is done.


By the way, daiginjo-shu (super premium ginjo made from highly-polished rice) shaves off more than 50%. Koji’s saccharification power is strong and its ability to break up protein is low. There is koji exclusively used for ginjo, that uses koji mold with refreshing taste. Preparation is thoroughly planned—for example, moromi is fermented for a long period at a low temperature—so that ginjo with fruity fragrance and delicate taste is produced.


There are various types of koji mold. You can get them for about 100 yen at grocery stores, but those packed in paulownia wood used exclusively for making ginjo, cost about 10,000 yen. When you open it there’s seed malt, and amongst them are those that have plenty of green koji mold spores attached to them. These bean sprout-like spores are sprinkled on steamed rice for two days and turned into white koji, which is used for preparation.


Koji mold is a lead player in Japanese food that is used in Japanese sake, mirin (sweet sake), soy sauce, miso (soybean paste) and amazake (sweet mild sake). As a matter of fact, it is used in purposes other than food from quite a long time ago. For example, it is used in Taka-Diastase, a medicine for digestion, which is also mentioned in Natsume Soseki’s novel, “Wagahai-wa Neko-dearu” (“I Am a Cat”). Professor Jokichi Takamine invented it over 100 years ago and is now used as an anti-indigestion tablet. Meanwhile, there’s an exogenous enzyme substance called lipase that removes oil stains in detergents, which is made up of genetically engineered molds that are made by using koji mold. This is now used worldwide.



Also, although there are very few reports on this, it’s known that koji mold has functions for enhancing health and beauty. I would like to spread this information to the Japanese people, so I launched a project called “Amazake Project” at Nihon Pharmaceutical University. Amazake is considered effective for atopic dermatitis and hay fever too. But it’s not known and valued amongst the overall Japanese people so there’s a huge gap. Yogurt, on the hand, is extremely popular today, and there’s a lot of study on lactic bacillus but for koji mold there’s only about 1/1000th amount of research done, which is a disappointment. So, we now have a goal for amazake to be produced and consumed by about 10 percent or more of yogurt by 2025. I truly believe that there are similar or even greater possibilities for amazake compared to yogurt, so I would like to contribute the rest of my life to koji mold and to study and spread it so that more people will get to know about it.


Katsuhiko Kitamoto is a research professor at Nihon Pharmaceutical University

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