Making Koji at Matsuse Shuzo (Shiga)

Matsuse Shuzo Toji Keizo Ishika dusting koji spores onto freshly steamed Yamada Nishiki rice.

We had the distinct pleasure to return to Matsuse Shuzo again this past February, this time, to watch the complete koji-making process! 

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.

We asked our mentor, Matsuse toji Keizo Ishida-san about the importance of koji and kojimai.

Why is koji the most important factor in sake-making? 
In sake production, 20% of the raw rice is made into koji, and the remaining 80% is steamed to make kakemai. This means that only 20% of the koji's enzymes are needed to break down 80% of the rice starch into glucose. Yeast ferments this sugar, breaking it down into alcohol and carbon dioxide—the mechanism of sake brewing.

Of course, the quality and performance of the koji can vary. The koji itself has a flavor, not just the dissolution of kakemai, and naturally there are pros and cons here as well. Kakemai itself, that is, rice that's simply steamed, doesn't have much flavor. It's simply a source of fermentation for the yeast.

To make it easier to understand, let's use the analogy of wine. Grapes have different flavors depending on the variety, and the sugar content varies depending on the vintage and terroir, and these are the roots of quality. With sake, it's safe to think of koji as being responsible for all of that. That's why it's important in every aspect, from fermentation to taste.

You referred to koji rice as "seed." Can you explain this a bit more?

First of all, the koji mold used in sake, or yellow koji mold, is a mold, a plant that does not photosynthesize. As such, koji mold has a life cycle of seed, germination, and flowering.

For us, the steamed rice used to make koji is simply called koji rice. We then sprinkle koji mold seeds, commonly known as bean sprouts, on the koji rice to encourage germination and flowering. This is called koji-making, or "seigiku."

The koji rice is broken down and taken out of the koji room just before it becomes seed or spores, which is called "dekoji."

The flower state of koji rice before spores form is called koji, and it is used in sake in this state.

What is the seimaibuai of koji rice?
It varies depending on the sake. For example, we reduce the amount of koji by 65% for junmai sake. For daiginjo, we reduce it by more than 50%.

Why do you always use Yamada Nishiki for your kojimai?
I value the consistent quality of the sake shipped from my company, so I always use Yamadanishiki koji to maintain the quality of the koji, which is paramount.

Kurabito (sake makers) spreading out the kojimai inside the Matsuse Shuzo koji muro (koji room)

A humid 87°F inside the koji muro

Monitoring koji growth 

Kojimai!

Verifying the growth of koji

Very healthy koji mold growth! They look like Q-tip heads

Inside the rice polishing room

On-site rice polishing machine

Different varieties of rice at varying seimaibuai (polishing)

The Raku series sake by Matsuse, which we are lucky to get here Stateside

Locals-only Matsuse sakes ready for delivery

A visit to one of Matsuse's rice fields

Examining the clay-rich soil which highlights the terroir of Omihachiman, Shiga, 

Thank you Ishida-san, as always, for your invaluable insight about koji, and for generously sharing with us your process.