The Part of Koji Making Where the Brewer Really Shines: The Fourth and Fifth Step to Make Good Koji: Naka-Shigoto / Shimai-Shigoto

Greetings Sake Lovers, welcome to another KURAND Magazine article that introduces you to the world of sake.

As a supplement to the recent Closeup of Production series, over the next few articles, we will be zooming into the various steps of the process and offering even more insight into how they are carried out. In this series, we look at koji making/seigiku. So far, In the previous articles, we explained how the brewer breaks up the rice to give the koji mold access to oxygen and then, after letting the koji rest a while, transfers it into smaller containers to control the moisture and temperature levels more precisely. Which brings us to the fourth stage, naka-shigoto and fifth stage, shimai-shigoto in Japanese.

Glossary
Koji = steamed rice with mold growing on it
Koji mold = the mold used to make koji
Seigiku = process of making koji
Haze = pronounced ha-ze describes the mold growth
Haze-guai = the state of haze
Kirikaeshi = breaking up, the second stage in koji making
Koji-muro = koji room
Koji-kin = Japanese word for koji mold
Shimpaku = starch filled core in the center of rice grain
Mori = mounding
Naga-shigoto = middle work
Shimai-shigoto = final work

What is Naka-shigoto / Shimai-shigoto?


The koji’s temperature increases during the 6-8 hours that it is left to sit following mounding. Next, the brewer moves the koji to a bigger table or container, or if using dividers removes these and spreads it out and folds it to help water evaporate and to increase the koji’s contact with oxygen. This stage is called middle work.

The koji is normally mixed by hand. It looks a lot like folding the mixture when you make a cake. Indeed, both naka-shigoto and that stage of cake making share the same purpose: to increase oxygen contact. If the steamed rice absorbs too much water, the temperature will not increase to the required levels and the koji will struggle to grow properly. After mixing, the koji is spread out. Ideally the brewer tries to remove any hills that have formed and get the koji level and may use a tool for this purpose.

6-8 hours after naka-shigoto, the temperature of the koji will increase again. The brewer has to step in to stop the koji from exceeding 40 degrees. This is the purpose of shimai-shigoto.

To help heat escape from the koji, some brewers draw a pattern or create furrows or ditches (like those you might see farmers create between their crops using a tractor) in the koji with their fingers. There is no real evidence that this helps, but each brewer has their own technique and they swear by it. The idea is that these furrows increase the surface area and speed up evaporation.

All of the target temperatures are decided beforehand so it is just a question of how the brewer achieves those targets. They may adapt their techniques depending on the condition of the rice which varies wildly year on year according to conditions during the growing season, and how the rice was washed, soaked and steamed.

Because temperature can fluctuate wildly from one moment to the next, it is necessary to keep a close eye on the koji and constantly check the temperature. Good koji is that which maintains a uniform temperature throughout; not too high and not too low.

It Is a Race against the clock


After reading the previous articles, you will no doubt now grasp the importance of temperature control in koji making. And the key to that control is speed. The brewer is constantly battling against the clock. A slow naka-shigoto and shimai-shigoto will result in the temperature falling too quickly, by too much. When dealing with large volumes of koji, the brewer also needs to exert a powerful control over the koji which is hard work. Even if machines are used, the final decisions are made by people. Some breweries that make sake on a large-scale use fully automatic machines that control the temperature. However, even at these breweries, the final decisions are made by toji, and it is still not yet possible to emulate the skill needed to make the best quality (tsuki-haze) koji for the best daiginjo.

Toji inspect the koji through sight, touch and smell; the inherent senses that only a human possesses. That is why even if a machine is used, they regularly have to check the koji and carry out adjustments by hand.

Naka-shigoto / shimai-shigoto is the Hardest Stage of Koji Making

Takahiro Suzuki toji of Kanbai-shuzou, which still uses futakoji (small box) method says that naka-shigoto / shimai-shigoto is the hardest part of the seigiku process. We asked him why.

Why do you think these stages are the hardest?

“There are times when I’m working in a 36 degree room for over an hour. In my company, there are no other employees trained to do this step so the task falls on my shoulders. Imagine working in a sauna. You don’t go there to work; you go there to relax. Naka-shigoto / shimai-shigoto are extremely draining physically and mentally. Also, I get very little sleep because I have to keep getting up to check on things.

Why don’t you just train your other staff to do this job?

It’s less a case of training someone up and more a case of someone have the time to master the skills required through practice and experience. During the regular brewing season, there simply isn’t the time to do this. If I can find people who trained at other breweries it might be a possibility to increase staff in future, but this is such an old- fashioned technique that there are very few people with these skills out there.


That about sums up the naka-shigoto / shimai-shigoto process. Just thinking about having to work in a sauna for an hour is enough to make most people sweat. Making good koji, especially the traditional way, requires a lot of experience and skill that you can’t earn overnight.

The next article will introduce the last step in the seigiku process: dekoji. This is not just taking the koji out. Traditional skills are used to make this happen. Check back next time to learn more about dekoji.

Until then, if you are in Tokyo, and fancy delving deeper into the world of sake, there is no better place than KURAND where you for just one price, you can taste over 100 different types of sake, carefully selected from boutique breweries up and down Japan, without time limits.
We look forward to welcoming you soon.