Mounding The Rice: The Third Step to Make Good Koji: Mori

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 article, we will look at koji making/seigiku. In the last article, article, we explained how the brewer breaks up the rice to give the koji mold access to oxygen, even out the temperature and moisture levels. The third stage is mounding or mori in Japanese.


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

What is Mori?

A large part of seigiku is a battle to maintain accurate temperature and moisture control. One very primitive but effective way of doing this is to alter the surface area of the steamed rice. This is the purpose of mori which literally translates to mounding. The process is called mounding because the brewer literally gathers all the rice into a mound.

Sometimes, for more precise temperature control which is required for producing more elegant styles of sake such as ginjo and daiginjo, the brewer first moves the rice into smaller containers.

Following the second stage, kirikaeshi, the koji mold is growing in a white spotted pattern that may or may not—depending on the haze—cover the surface of the grain.

As the koji mold grows, it gives off heat. If the temperature is allowed to continue increasing, it may reach a point where it stops the growth of the koji mold or worst, kills it—and dead koji imparts undesirable flavors and aromas into the fermentation—thus the stacked rice is loosened up by hand and sometimes a portion of it is moved into smaller containers. As heat rises, the brewer stacks the smaller containers on top of one another and has to switch their order constantly. The trays have to be rotated every 2-3 hours. The people tasked with looking after the koji are called koji-ban (literally, koji shifts) and get very little sleep. You might rather daringly compare this routine to child rearing, but we are by no means trying to belittle the latter.

Three Methods of Mori

There are three methods of mori: futa-koji, hako-koji, and machine mounding.

Futa Method
Futa-koji is the most traditional of the three methods, but it is also the most time-consuming and labor intensive. A futa is a small wooden tray that looks like a wardrobe drawer, measuring about 200cm x 200cm and holding 1.5kg of rice each. It Is not uncommon for as many as 100 of these small trays to be used in any one brewing batch and cleaning them as just as much work as using them. The hardest part, and where the brewer gets to show off a little, is the task of getting the rice into the center—something akin to that game where you have to steer balls through a wooden labyrinth and into holes—by tilting the tray in all four directions with sudden but well-timed flicks of the wrist. The most skilled brewers can complete this task in an impressive 5 seconds or less.

Hako Method
A hako (box) is a large version of the futa, measuring about 150cm long, 85cm wide and 18cm (source: sake glossary by Nada Sake Research( deep and holding around 15kg. This method is not as labor intensive as the futa method, so this tends to be the preferred method. However, it is difficult to achieve the precision of the futa method with hako.

Machine Method
There are machines that automate the mounding. The machine automatically adjusts the temperature and moisture in accordance with the growth of the mold.

The Secret Behind the Futa Method

When it comes to precision, despite advancements in technology, the old method still wins hands down. Machines get close, but they lack that human touch required to adapt to the changes in the consistency of the rice, the ability of which is considered to be the key to achieving the target quality. And that’s why most breweries still honor the old method.

It’s All in The Cedar

Another reason why the futa method is so much more effective is to do with the material the futa are made from cedar or sugi in Japanese. Historically, sugi was a common material in-house building because it can absorb a large amount of water reducing damp. A 10cm block of sugi can absorb about (1800cc) bottle of water. Sugi performs the same role in the futa method, drawing precisely the right amount of moisture away from the inoculated steamed rice.

The high water absorbency is also the reason that many sakaguras (breweries) make their koji-muro out of sugi. It also helps to maintain a warm drying environment even in the middle of winter.

Ask The Brewer

We wanted to find out why, In a modern age where sake brewing is becoming more and more mechanized, brewers still opt for sleepless nights, so we decided to ask a brewer.

This is the answer we received from toji Takahiro Suzuki of Kanbai-shuzou in Saitama prefecture, who make all their sake by the futa koji method.

What is the most challenging part of the futa method? 
“That would be the fact that you have to make multiple batches of koji, all at the same temperature and the same haze-komi-guai. Dividing up and managing in futa, enables me to keep the temperatures uniform across batches.”

“Someone must be there the whole time to manage the temperature, so it’s not just challenging but also extremely labor intensive. It is true that I often don’t get enough sleep some nights because I have to keep getting up to check on the koji.
Experience plays a big part in being able to brew good sake with the futa-koji method, which I still lack, so brewing daiginjo sake by the futa method is nerve-racking.”

Futa-koji seems to be very hard on the body and mind Why then would you go to all this trouble to brew sake?

“Simple! I enjoy the challenge and being able to be more closely involved with the brewing process. Yes, it’s hard work, but there is a sense of satisfaction at the end that you don’t get with the more modern hands-off methods, you develop deeper feelings for the end product, which in turn, motivates you to produce better sake.

I will keep working hard to build up my experience so that I can make even more delicious sake in the future.”

So there you have it, that about wraps up this article. Brewers aren’t opting for traditional more labor-intensive methods because they like the extra work; they do it to feel more closely involved with their craft. It makes sense that they would care more for the end product if they had to go through all those sleepless nights. If only it were possible to translate this feeling through the end flavor. Perhaps the sake of the future will do precisely that.

The KURAND concept is that sake tastes even more delicious when you know who made it and how. And that’s why we write these articles. Why not come and experience the devotion that goes into every bottle of sake yourself. With over 100 different types of sake, carefully selected from boutique breweries up and down Japan, you are sure to

In the next article, we will look at the fourth stage in seigiku, nakashigoto (middle work).