Kojimai (August 2025)

Howdy! Kayoko here, Yoko’s other half. I’ll be taking over Sake Gumi for the next two installments, exploring the wonderful world of koji with you all. This is an incredibly dense subject and I hope to be able to explain myself in simple terms. This month, I’m exploring the theme of kojimai, which will cover the more technical aspects of sake production and creating koji in sake.

First, what is koji? Koji is Japan’s national mold and is a key ingredient in Japan’s most prized pantry items like soy sauce, miso, and sake. Its chief duty is to create glutamic acid, which is what we know as umami, or savoriness. This glutamic acid becomes the usuable sugar for alcohol fermentation.

Next: what is kojimai? Kojimai is rice that has been inoculated with the koji mold. Spores of koji, in powder form, are sprinkled onto rice and are grown onto the rice meticulously over a 40-50 hour period until the kojimai is ready.

In sake production, most brewers would say that the kojimai is the most important ingredient in the sake (shochu makers would say this too!), so many go through the painstaking method of making their own kojimai. When reading the back of a sake label, you might see a certain rice for kojimai, and another for kakemai. Kakemai is the majority of the rice used when making sake – but kojimai has to account for at least 15% of the total rice used. Sometimes, brewers use the same rice for both kojimai and kakemai, others opt to use differing varieties.

Koji inoculated Yamada Nishiki rice at Matsuse Brewery

Brothers Kazuki and Masato Usui, the brilliant brewer and toji combo of Senkin Brewery says, “The enzymes produced by koji rice are directly linked to the quality of the sake. While kakemai is the main sugar source for fermentation and has a relatively mild effect on the taste, koji rice is the basis for enzymes, saccharification, and umami, so it has a huge effect on the taste, making it very important.”

This theme of kojimai came to me while Yoko and I were helping make koji at Matsuse Brewery in Shiga this February. Our mentor Keizo Ishida, toji of Matsuse, told us that kojimai was paramount – it is like the seed and the kakemai is the water. Which is to say that the kakemai is only there to support and unlock kojimai’s vast potential.

Kanpai,
Kayoko
Co-Founder + Shochu Director, Umami Mart

SILVER + GOLD

Cuvee Ying Ying Tokubetsu Junmai
Matsuse Shuzo (Shiga, Japan)
Kojimai: Yamadanishiki
Kakemai: Yamadanishiki, Ginfubuki, Nihonbare, Wataribune
Seimaibuai 65%, SMV + Acidity: Undisclosed

Ishida-san always uses Yamada Nishiki for his kojimai, explaining: “I place the utmost importance on the stability of the quality of the sake shipped from my company, so I always use Yamada Nishiki koji to maintain the quality of the koji.

We love this wonderful, summertime, low- ABV sipper with high acidity, reminding us of a glass of an off-dry Riesling. Get notes of juicy melon and lush pears, while letting the bright aromas and acidity dance on your palate. Enjoy chilled with halibut ceviche or simply with a bowl of lychees and grapes.

Senkin Nature Kimoto Kioke Muroka Nama Genshu Junmai
Senkin Sake Brewery (Tochigi, Japan)
Kojimai: Kame No O, Kakemai: Kame No O
Seimaibuai: 90%
SMV + Acidity: Undisclosed

If there were a category of natty sakes, Senkin would be one of its originators; and this sake would be its prized flagship bottle. Senkin is inspired by the vin naturel movement and concepts of terroir in sake.

The local rice Kame No O is organic and pesticide-free, and is used both for the kakemai and kojimai here. Brothers Masato and Kazuto Usui says, “Kame no O is less soluble than Yamada Nishiki. When used to make koji rice, the koji mold slowly and thoroughly penetrates the rice, making it easier to produce koji rice with strong enzymes. Kame no O has the advantage of not producing many unpleasant flavors after polishing. This brings out a clear flavor. Using it to make koji rice brings out the umami and fullness of the rice, and adds depth to the aroma.”

Get notes of crisp green apple and a creamy, earthy finish. Enjoy chilled in a wine glass with a slice of anchovy toast.

Kioke wood casks at Senkin