Photo by Denen Shuzo
Koji is a crucial ingredient used in the production of shochu, a traditional Japanese distilled spirit. And among the three strains of shochu koji: black koji is arguably the most significant.
This article explores black koji, its history, shochu production with black koji, its flavor profile, and more.
What is Black Koij?
Black koji (kuro koji, 黒麹菌) is a mold spore that breaks down the starch in the main ingredients in shochu production into sugars that yeast can ferment into alcohol. Sweet potato, long-grain rice, and short-grain rice are the most well-known base ingredients for kuro koji but aren’t the only ones.
Of the three koji used for shochu production, kuro koji produces the richest and most distinctive shochu.
Recently, black koji was reclassified from Aspergillus awamori to Aspergillus luchuensis. And white koji, a mutation of kuro koji, was reclassified as luchuensis, as well.
History of Kuro Koji
Black koji’s roots can be traced back to Okinawa and awamori. The mold spores grow readily on long-grain (Thai) rice. And the kuro koji and long-grain rice combo have been used for centuries.
But it wasn’t until around 1910 that black koij was used for shochu production outside of Okinawa. Before then, yellow koji, used for sake production, was utilized instead. This type can work for shochu production, especially with rice, but it produces low acidity, and fermentations often spoil.
Genichiro Kawachi and Kensuke Kanbe, engineers from Kagoshima, popularized the use of black koji for sweet potato shochu after studying the fungi’s high production of citric acid. The acidity it produces shields the moromi from spoilage and significantly improves shochu quality and yield.
The use of black koji for shochu production quickly spread to other regions and ingredients.
Shochu Production with Black Koji
Rice, barley, sweet potato, and soba can all be used as a koji base, but rice is the dominant choice.
Large shochu distilleries will have rice steamers, soaking tanks, rice cooling machines, and dedicated koji-making machines – just like sake breweries. But many distilleries don’t have this equipment.
Historically, shochu koji was made just like sake koji using the tray, box, or table methods. But in 1961, the rotating drum automatic koji maker and the semi-automatic koji-making machine (sankaku dana) were introduced, allowing for automation.
Larger distilleries often use more efficient and modern equipment and techniques to make koji. But many smaller distilleries still use traditional processes similar to koji-making for sake.
Shochu production typically starts with ichiji-moromi (first-stage moromi), the equivalent of shubo for sake. All koji is added during ichiji-moromi in shochu production. The second stage of shochu production, niji moromi, is equivalent to the moromi phase in sake brewing. The main ingredients (like sweet potato and barley) are added during this second stage.
Rice and Barley Koji Production
Rice is the dominant base ingredient for shochu koji production. It’s generally polished to 90% (10% removed) before koji-making, though in some cases, it’s polished to ginjo levels (60% or less). Non-glutinous (sticky) varieties are used.
The process of using barley is much the same as with rice.
Many distilleries use the compact and economical rotating drum, where washing, soaking, steaming, and koji-making take place. Some distilleries will remove the rice or barley and finish the koji-making process in a semi-automatic koji-making machine (sankaku-dana). Others will finish the koji making in the drum.
Sweet Potato Koji Production
Sweet potato koji is a newer development championed by Takara Shuzo and their Ikkomon brand.
The sweet potatoes are cleaned, trimmed, diced, then dried to pregelatinize them and reduce the liquid content. Only then can sweet potato koji be propagated.
Dirty Black Koji
Black koji often covers the interior of distilleries and the workers’ clothing. Care is taken not to clean too much or disturb the ambient koji. Because of this, some distilleries appear dark and dirty.
White koji became popular for shochu production in large part because it’s easier to keep everything clean.
Black vs White and Yellow Koji
Black and white koji produce high amounts of citric acid, which safeguards the fermentation against spoilage. These “shochu koji” handle the acidic environment better than sake koji.
To better understand the differences between the different types of koji, here is a table to compare them:
| Type of Koji | Color | Spores | Brewing Characteristics | Flavor |
| Kuro-koji | Black | Black | Readily grows on Thai rice and produces high citric acid and strong enzymes for saccharification | Rich flavor, slightly sweet, strong, complex, and fragrant aroma |
| Shiro-koji | White | Orange-amber | Quickly converts starch to sugar due to high enzyme power | Rounded texture, sweet, mild or sharp flavor, muted aromatics, but Ginjo-like |
| Ki-koji | Yellow | Yellowish-green | Strong enzymes to saccharify starch and break down protein, highly fickle, and temperature control is very challenging | Light, smooth texture, very aromatic, with fruity and citrus-driven aroma; refreshing |
Flavor Profile of Black Koji Shochu
Kuro koji tends to make shochu with a fragrant aroma and rich flavor. Acidity is often elevated, which can result in a sharp finish. Kuro koji is also capable of making shochu with great complexity. Funky and citrusy notes are common too.
In comparison, white koji shochu tends to be a little more restrained in aromatic and flavor intensity. It tends to produce a softer textured shochu, as well. Yellow koji shochu is often quite elegant, fruity, and supple. But it’s rare due to the difficulty of fermentation.
Black Koji Shochu Brands
A significant number of shochu brands are made with kuro koji, including all brands of awamori and many sweet potato shochu brands. The word ‘kuro’ is typically an indication that black koij is used.
Popular kuro koji sweet potato shochu brands include Kuro Kirishima, Kozuru Kuro, Satoh Kuro, Kaido Iwai no Aka, and Shiranami Kuro. And look out for Mizuho Awamori, Chuko Kusu, Harusame Kari, Zuisen Hakuryu, and Yonaguni brands of traditional-style awamori.
Other types of shochu made with black koji are much harder to find, as white koji is the defacto choice for rice and barley shochu.