Dr. Shimoda’s New Theory of Honkaku Shochu – Vol. 5

⇒ Vol. 4: “Second Moto, Third Brewing” Part 1 — Primary Fermentation: Propagating Yeast, the Moto of Fermentation

As told by: Masahiko Shimoda, Advisor, Sanwa Shurui Co., Ltd. / Composition: Kenji Inoue, Contentsbrain

In the previous installment, we discussed Step 4, “primary fermentation,” which corresponds to “second moto” in the production process of honkaku shochu. We introduced techniques for preventing spoilage during fermentation, as well as the conditions favored by yeast, the central player in fermentation.

This time, we will discuss Step 5, “secondary fermentation,” which corresponds to “third brewing.”

Step 5: Secondary Fermentation (Second Shikomi) 
The Emergence of Honkaku Shochu’s “Secondary Fermentation Method” 120 Years Ago

In sake brewing, moto making was established around 300 years ago through a method known as kimoto making, which developed during the Edo period.*1

* 1 Edo period: A period of long-term rule in Japan that lasted from the early 17th century to the late 19th century. Systems for governing the country were put in place, and almost no major wars occurred. It was also a period when urban populations grew and popular culture developed.

Kimoto making is a method that harnesses the power of nature while suppressing the growth of contaminating microorganisms that are harmful to brewing. Chilled water is used during the harshest winter months, and alcoholic fermentation of the moromi* 2 is promoted while the temperature is gradually raised. It is an ingenious mechanism that controls the rise and decline of microorganisms solely through temperature control.

* 2 Moromi: A state in which koji, water, yeast, and other ingredients have been added to a fermentation tank and are then fermenting.

However, in southern Kyushu, which is located in the south of Japan where temperatures are higher than other regions, it was difficult to reproduce this kimoto making process. Even so, until 120 years ago, honkaku shochu production had no choice but to follow the sake brewing model used in colder regions. The method of adding rice koji, the main ingredient, and water to a shikomi vat or earthenware jar was the same as the moto used in sake brewing. However, whereas rice was the ingredient used in sake brewing in colder regions, in southern Kyushu, barley, sweet potatoes, and miscellaneous grains that were widely available locally were used instead and fermented in a single stage. Steamed sweet potatoes in particular allow various unwanted bacteria to begin proliferating immediately after preparation, and producers appear to have struggled to prevent spoilage.

Establishing a Stable Brewing Method for Warm Regions through the Secondary Fermentation Method and Black Koji Mold

After much trial and error in sweet potato shochu production in Kagoshima, at the southernmost tip of Kyushu, the secondary fermentation method emerged in 1903. Instead of adding rice koji, steamed sweet potatoes, and water all at once, producers arrived at a method of separating the koji and the main ingredient. In other words, rice koji and water were added in the first stage, and steamed sweet potatoes and water in the second.

By increasing the yeast population and raising the alcohol concentration during primary fermentation, producers were able to suppress the risk of unwanted bacterial growth and spoilage during secondary fermentation, when the main ingredient is added, making brewing more stable and reliable. This was against the backdrop of the introduction of a licensing system for alcoholic beverages as a foundation of national finances after home brewing was prohibited in 1899, along with the consolidation of producers and the modernization of production sites.

What brought the secondary fermentation method for honkaku shochu closer to perfection was the use of black koji mold, rather than the yellow koji mold used in sake brewing. Following the introduction of microbiology from the West during the Meiji period, * 3 black koji mold was first isolated in 1901 from the koji used in awamori produced in Okinawa. Studies of its properties revealed that black koji mold produces large amounts of citric acid during koji making, powerfully protecting against the intrusion of contaminating microorganisms and proving effective in preventing spoilage. Around the same time that the secondary fermentation method became established in sweet potato shochu production, shochu makers in Kagoshima began using this Okinawa-born black koji mold from 1912.

* 3 Meiji period: In the late 19th century, Japan’s feudal Edo period, which had lasted around 200 years, came to an end, a new government was established, and the Meiji period began. Western science and technology, culture, and ideas were actively adopted as Japan sought to become a centralized modern nation.

The adoption of the secondary fermentation method and black koji mold established a stable and reliable brewing method unique to honkaku shochu. It is an ingenious mechanism, no less impressive than the traditional kimoto method used in sake brewing, that skillfully utilizes and controls the properties of microorganisms.

Secondary Fermentation Is the Source of Honkaku Shochu’s Diversity

The secondary fermentation method and the use of black koji mold became established as the production method for sweet potato shochu and gradually came to be used in the production of other types of honkaku shochu, including rice shochu and barley shochu. In other words, the primary fermentation process, in which only rice koji, water, and yeast are added, became standardized, while different main ingredients, such as sweet potatoes, rice, and barley, are added during secondary fermentation.

In addition to grains, tubers, sake lees, and kokuto sugar (brown sugar), the ingredients that can be used in secondary fermentation for honkaku shochu now include 49 items designated by the Commissioner of the National Tax Agency, such as sesame, chestnuts, and carrots. As a result, honkaku shochu has become a one-of-a-kind distilled spirit with a diversity found nowhere else in the world.

Japan’s Liquor Tax Act permits 49 items designated by the Commissioner of the National Tax Agency, as listed above, to be used as ingredients in honkaku shochu, in addition to rice, barley, sweet potato, buckwheat, sake lees, and kokuto sugar.

If the main ingredient added during secondary fermentation is sweet potato, it is called “sweet potato shochu”; if it is rice, “rice shochu”; and if it is kokuto sugar, “kokuto sugar shochu.”

As a side note, Sanwa Shurui’s barley shochu iichiko, or mugi shochu in Japanese, uses barley koji rather than rice koji in primary fermentation, and also uses barley as the main ingredient in secondary fermentation. It is therefore described as “100% barley honkaku shochu,” distinguishing it from barley shochu made using rice koji in primary fermentation.

⇒ Vol. 4: “Second Moto, Third Brewing” Part 1 — Primary Fermentation: Propagating Yeast, the Moto of Fermentation

Main references: Honkaku Shochu Seizo Gijutsu (Honkaku Shochu Production Technology, Brewing Society of Japan, 1991); Sake-zukuri no Hanashi (Stories of Sake Brewing) by Yuichi Akiyama (Gihodo Shuppan, 1983); Hakko to Jozo II (Fermentation and Brewing II), edited by Kazuo Azuma (Korin Publishing, 2003); Sekai no Spirits: Shochu (Shochu: Spirits of the World) by Akira Sekine (Gihodo Shuppan, 2005); Shochu no Rirekisho (The Resume of Shochu) by Yoshihiro Sameshima (Ikaros Publications, 2020).