1. Steaming softens the material, allowing the koji mold to grow more easily.
Koji Guide
Koji-kin: The basics
Koji (Aspergillus oryzae) is a fungal spore cultivated by only a few companies across Japan. It is most commonly produced using rice, but can also be created with buckwheat (soba), sweet potato (imo), or barley (mugi), as part of a painstakingly complex process requiring attentive care and expertise.
The use of koji stems from the main ingredients used to make shochu; nearly all of them contain copious amounts of starch and virtually no sugar--a necessary element to produce alcohol during the fermentation stage of production. Without this step, the production of alcohol would be impossible due to the inability of the raw materials to ferment when mixed with yeast.
Rice has long been the standard for koji because of its versatility; however some shochu manufacturers use sweet potato, buckwheat, or
barley to make koji. Typically, when a material other than rice is used to make koji, that same material is often the base ingredient used to make the resulting shochu.
After 12 hours in the “koji room,” it is divided into equal parts and placed onto flat trays in the “koji room.” The issue of temperature and humidity consistency still applies, so mixing the koji and rotating the trays every few hours is necessary until propagation has been achieved.
Alternatively, the koji can be spread out on a large table, about the size of a billiards table, during this stage.
The process to create koji can take anywhere from 40 to 50 hours and has four basic steps: washing and steaming the material, applying the tane-kin, proliferation of spores, and cooling.
2. Tane-kin is applied to the steamed material. The tane-kin powder is sprinkled over the base material by hand (as shown), or with a sifter or similar device.
3. The soon-to-be koji is mixed thoroughly, then wrapped in a cloth and placed into a special “koji room.” With the “koji room” being so hot and humid, the cloth helps retain both warmth and moisture. In addition, as the spores breed an abundant amount of heat is generated, requiring the koji to be stirred in order to regulate temperature.
4. To conclude koji production, the trays are simply removed from the “koji room” and allowed to cool at room temperature. Once cooled, the koji is ready to be used in the shochu production process.
The Colors of Koji: What do they mean?
Once the koji has been produced, it is then mixed with yeast and water to create what is called the primary moromi. At this stage in the production process of shochu, the yeast and glucose react together to trigger fermentation and the formation of alcohol. The impact koji has on the finished product is enormous. The effects koji has on the aroma and flavor of shochu allows each shochu producer to differentiate their final product from those of their myriad competitors.
Koji comes in three different forms: kuro (black), shiro (white), and kii (yellow). Koji is classified by these three colors because of the final appearance of the koji after the mold is bred onto the base material. The different types of koji not only bring about a difference in color, but also yield distinct characteristics that shape the flavor and aroma of each shochu produced.
Black (kuro) koji
Historically, kuro-koji originated in Okinawa for the production of Awamori, and is still used today to produce most Awamori. In 1910, kuro-koji was first brought to mainland Japan via Kyushu. It was introduced by Genichiro Kawachi in an effort to provide local shochu producers with a high quality koji that was more sustainable than yellow (kii) koji. Kuro-koji is more durable, thus more suitable for the subtropical climate most shochu is produced in. Despite being able to produce exceptionally flavored shochu, most makers eventually phased out kuro-koji due to sanitary concerns.
In 1985, Masaaki Yamamoto developed NK-koji, a more palatable form of kuro-koji. This NK-koji was first implemented in the production of the Kuroisa Nishiki shochu brand in 1987. Kuro-koji shochu is typically intense in flavor and aroma. The flavors range from earthy to sweet, smoky to smooth. Sweet potato (imo) shochu and Awamori are most commonly produced with kuro-koji.
White (shiro) koji
Shiro-koji was the last shochu koji to be developed. Shiro-koji was discovered in 1923 when Genichiro Kawachi (the man who introduced kuro-koji) witnessed a mutation in kuro-koji. This led to further research until he could determine how to cultivate it independently. Shiro-koji eventually replaced kuro-koji in an effort to thwart the horrendous sanitary conditions caused by kuro-koji. Producers realized a number of benefits from using shiro-koji: durability, ease of propagation, and boosted sacchrification. It still dominates the shochu industry, but not as strongly since the inception of NK (new kuro) koji.
Shiro-koji is highly versatile and can be used with basically any raw material: sweet potato (imo), barley (mugi), rice (kome), Japanese basil (shiso), and etcetera. Shiro-koji shochu are typically easy to drink and bear quite mild and clean characteristics, which is why it often recommend to those who don’t care for strong or earthy flavors.
Yellow (kii) koji
Kii (yellow) koji has existed in Japan for many years and even predates the production of shochu. It was originally used in the production of Japanese sake but was soon adopted in the production process of shochu due to the need for koji.
Kii-koji is highly sensitive to temperature and is best suited for cooler climates. With most shochu production taking place in the subtropical climate of Kyushu, kii-koji eventually went out of fashion in the 1920s. After its abandonment, kii-koji was seldom used until shochu boomed in
the early 1990s. In recent times, the use of kii-koji is slowly increasing, but on a very limited basis.
Like shiro-koji, a variety of raw materials may be used in conjunction with kii-koji: rice (kome), sweet potato (imo), barley (mugi), and etcetera. Shochu produced with kii-koji is often noted as being crisp and refreshing with light and fruity undertones. Many purveyors of shochu note that the majority of patrons who order kii-koji shochu are women.