Rare Blog of a Novice Brewer

This article provides an easy-to-understand guide on how to make sugar-free fermented anko (sweet red bean paste) using a rice cooker, yogurt maker, or pressure cooker. It also covers the benefits, ways to enjoy it, and tips for foolproof results, making it a comprehensive resource. Additionally, we will share insights from a brewery's perspective on the key points for choosing rice koji, which greatly influences the finished product.

Introduction: "Rice Koji" is the Foundation of Japanese Food Culture Sake, miso, soy sauce, mirin, shio-koji, amazake – none of these would exist without "rice koji." Rice koji is the unsung hero that supports Japan's food culture, a nation of fermented foods. As a sake brewery, we prepare a large amount of rice koji every year. Koji-making is not merely a manufacturing process; it's a dialogue with microorganisms called koji mold, and the very essence of craftsmanship passed down through generations. It is said that the process of koji making is where humans assist koji mold to create a comfortable environment for it to grow, as the seed koji attaches to the surface of steamed rice, extending its hyphae towards the internal moisture and proliferating on the surface. The Difference Between 麹 and 糀 Both characters represent koji mold and are often used interchangeably depending on the context. ･糀 is a Japanese-created kanji character, derived from the appearance of koji mold blooming like a "flower" on steamed rice. It often specifically refers to "rice koji" used in making miso and soy sauce. ･麹 is a kanji character introduced from China, often representing koji from all grains, and is primarily used in sake brewing. What is Rice Koji? Definition and Basic Knowledge Koji Mold "Aspergillus oryzae" Rice koji refers to steamed rice on which koji mold (Aspergillus oryzae) has been propagated. Koji mold is a type of fungus, but it is not only harmless to humans but also known as a beneficial microorganism essential for food fermentation and brewing. It is also a microorganism indigenous to Japan, and on October 12, 2006, it was recognized as Japan's "national fungus" by the Brewing Society of Japan. From an academic perspective, the genome of Aspergillus oryzae was sequenced in 2005 (by the National Institute of Advanced Industrial Science and Technology), and it was found to possess approximately 12,000 protein-coding genes. Compared to its close relative, A. flavus, koji mold has genes that produce toxic aflatoxins silenced (inactivated), confirming its high safety at the genetic level (Machida et al., 2005, Nature). In other words, koji mold is "a safe and excellent microorganism that Japanese people have selected and cultivated over a long history," and it does not naturally exist in environments outside of Japan. The "Power of Enzymes" Created by Rice Koji - The Most Important Function for Breweries For sake breweries, the greatest value of rice koji lies in its being a treasure trove of enzymes. As koji mold extends its hyphae, it secretes a wide variety of hydrolytic enzymes. Amylase = Converts starch into sugar. Amylase is an enzyme that breaks down starch (polysaccharides) into glucose and maltose. In sake brewing, this reaction enables a unique fermentation process called "multiple parallel fermentation." Beer undergoes sequential fermentation, where barley starch is saccharified before fermentation. Wine is made by fermenting grapes, which are naturally rich in sugar. In sake, the saccharification of rice starch by koji and the alcoholic fermentation by yeast proceed simultaneously. This multiple parallel fermentation is one of the reasons why sake achieves a high alcohol concentration of nearly 20 degrees while possessing complex and delicate flavors. Protease = Converts protein into amino acids Protease is an enzyme that breaks down proteins into amino acids. Amino acids such as glutamic acid, which are at the heart of sake's "umami," are produced by the action of this protease. Sake breweries often use the term "koji no chikara" (power of koji), which precisely refers to the strength of these enzymatic activities. If the koji's power is too strong, the sake becomes too sweet; if it's too weak, fermentation doesn't proceed. The koji master discerns this delicate balance through decades of experience and intuition. Lipase, Cellulase, etc. Koji mold also produces various other enzymes such as lipase, which breaks down lipids, and cellulase, which breaks down cellulose. These act in combination to create the diverse flavors and nutritional value of fermented foods. Koji Making Process: The Craft of the Sake Brewery Koji Production Process ① Selection and Polishing of Raw Rice Good koji starts with good rice. Sake-brewing suitable rice varieties like Yamadanishiki and Gohyakumangoku have a shinpaku (white core), a central starchy part, which makes it easy for koji mold to propagate. Since the polishing ratio also affects the quality of the finished koji, this step is extremely important. ② Washing, Soaking, and Steaming The polished rice is washed, soaked in water for an appropriate time, and then steamed in a steamer (koshiki). The ideal steamed rice is "gaikou nainan" (hard on the outside, soft on the inside). This allows the koji mold to easily extend its hyphae into the interior. ③ Spreading Seed Koji After cooling the steamed rice to an appropriate temperature (approx. 35-40℃), seed koji (spores of koji mold attached to a carrier) is sprinkled evenly. Currently, seed koji is manufactured and sold by specialized業者 called "moyashi-ya" (seed koji makers), with a history dating back to the Muromachi period. ④ Management in the Koji Muro: The True Skill of the Craftsman In the koji muro, where temperature and humidity are strictly controlled (35-40℃, approx. 90% humidity), the hyphae are propagated over approximately 48 hours. During this time, brewers "teire" (tend to) the rice by hand every few hours to equalize the temperature and control the growth of the hyphae. Entering the koji muro at 2 or 3 AM is a reality of sake brewing. To make good koji, "sleepless vigilance" is literally required at times, and the brewers' hands are always warm, imbued with the sweet aroma of rice. The optimal temperature for koji mold growth is approximately 30-35°C for hyphal growth and 25-30°C for spore formation. While master brewers of the past understood this through experience, our brewery manages the optimal timing for tending and room temperature by managing data with IoT. Health and Nutritional Benefits of Rice Koji: The Scientifically Proven Blessings of Fermentation In recent years, rice koji has also gained attention as a health food. Production of Vitamins and Essential Amino Acids Through the metabolism of koji mold, B vitamins (B1, B2, B6, niacin, etc.) are produced. Furthermore, the amino acids produced by proteases include essential amino acids, increasing its nutritional value. Presence of Functional Peptides Fermented foods derived from koji have been reported to contain ACE-inhibitory peptides that have blood pressure-lowering effects (Itou & Akahane, 2004, and others). Scientific evidence like this is behind the attention given to shio-koji and amazake as health foods. Reference: From the Consumer Affairs Agency's "Status of Analysis after Notification of Foods with Function Claims" Impact on Gut Environment Polysaccharides and peptides derived from koji mold in koji-fermented foods are suggested to contribute to the improvement of the gut microbiome (gut flora). With the recent advances in gut microbiome research, the focus on the functional properties of fermented foods is further increasing. Types and Uses of Rice Koji: Explained from a Sake Brewery's Perspective The properties of koji vary greatly depending on the strain of koji mold and culture conditions. Yellow Koji (Kikouji): The Main Player in Sake, Miso, and Soy Sauce This is the most widely used koji. Since it produces less citric acid, it results in sake with low acidity and delicate, fruity characteristics during brewing. White Koji (Shirokouji) and Black Koji (Kurokouji): Giving Shochu its Character Koji traditionally used in shochu brewing in Okinawa and Kyushu regions. It produces a large amount of citric acid, which is effective in preventing contamination by miscellaneous bacteria. Black Koji (Aspergillus luchuensis) is the traditional koji for Awamori, and white koji was discovered as a mutant strain of it. In recent years, there have been increasing efforts to apply white koji to sake brewing, and "white koji-brewed sake" with a sharp acidity different from traditional yellow koji has become a topic of discussion. The Future of Koji Making from a Sake Brewery's Perspective I believe that traditional handcrafted koji-making will continue to retain its value. However, at the same time, advancements in science and technology also offer new possibilities for koji research. Research on improving functionality using koji mold genome information, and at our brewery, while various sensors manage temperature and humidity, major companies are developing automated koji muro management systems utilizing AI and sensor technology. The integration of tradition and innovation is progressing. What we value is using our hands with a scientific understanding. We trust the numbers displayed by temperature sensors and data loggers, but ultimately, we make judgments by smelling the koji, touching it with our hands, and observing its color. That is the job of a sake brewery's master brewer. Conclusion: Rice Koji is a "Living Cultural Asset" Rice koji is not merely a tool for fermentation. I believe it is a "living cultural asset" that has been cultivated over hundreds of years in Japan's climate and passed down from craftsman to craftsman. Koji mold Aspergillus oryzae is Japan's "national fungus," with its safety and functionality proven at the genomic level. Rice koji supports the world's only brewing technique of multiple parallel fermentation, producing the taste, aroma, and nutrition of fermented foods through its rich enzyme group, including amylase and protease. Koji making is a precise technique that combines the management of temperature, humidity, and time with the five senses of the craftsman, and scientific research on its health functional properties is also rapidly progressing. For a sake brewery, koji is the "beginning of brewing" and the "life of sake." Next time you pick up sake or miso, I hope you will give a little thought to the work of the koji masters behind it and the unseen activities of the microorganisms.