Closeup of Sake Production: Shubo

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

So far in this series taking you on a tour of the sake production process, KURAND Magazine has looked at how the brewer prepares the rice, polishing, washing, soaking and steaming it before malting it to create koji in the seigiku stage. A batch of that steamed rice is now taken to a special room to create something called the shubo. You may remember that we explained that the 1,2,3s of sake brewing are koji, moto, and moromi. Moto (origin or base) is another word for the shubo, so in other words, we are about to dive into the second most important stage in the process.

Sake Making in a Nutshell

A very basic diagram of the sake brewing flow can be found in the chart above. This is just a very basic outline. The process varies depending on the variety of rice and the target style of sake.

What is the Shubo?

Shubo is basically a mini-fermentation, a starter or seed mash where the yeast is propagated or bred into a big enough healthy population to facilitate the rest of the fermentation process. Without a large enough population of yeast, the fermentation may stop prematurely or become contaminated by wild bacteria or yeast because the yeast cannot defend itself in small numbers. But what is the yeast defending itself from? you may ask.

A very key difference with other fermented beverages is that the tank in which sake is fermented does not have a lid. The nutrient-rich mash is an open invitation to wild bacteria and other microbes and to those bacteria, a sake mash is the nutrient shake from heaven. If the yeast is eliminated, the wild bacteria will take hold of the moromi and spoil it, a condition called fuzo (literally, rotten mash) in Japanese.

The size of the shubo tank is a 10th (600l) of the fermentation tank (6000l). If the yeast was thrown straight into a large tank, the sheer volume of ingredients and space would overwhelm it and it would struggle to propagate.

Sokujo vs Kimoto

The shubo is basically a battle for survival among microbes and it is the brewer’s job to insure the yeast comes out as the victor. Wild bacteria and other microbes have no problem surviving the conditions of the fermentation tank that is except for one condition: acidity. In general, microbes have a low tolerance for acidity. But yeast is a different beast in that it is able to survive high acidity. So all the brewer has to do to give the yeast an advantage and the other microbes a handicap is to raise the acidity levels in the shubo. The modern way to do this is to add lactic acid. There are two methods to add lactic acid.


The easiest way to add lactic acid is to do just that, add it. This is the way the modern shubo is made. Sokujo is a very fast method of making the shubo. It takes just 14 days. This method also produces the most consistency and balance of flavor.


Back in the early days of brewing, brewers lacked the scientific knowledge to understand why the shubo worked. They didn’t yet fully comprehend the relation between acidity and the yeast. But somehow, perhaps through trial and error, they developed a method to create the shubo.

This method is called kimoto. This method is all about exploiting the lactic acid bacteria that congregate around the tank when the conditions are right and eventually fall into it. In this method, the lactic acid is not added but created by these bacteria. The first challenge is enticing them into the tank. Generally, lactic acid bacteria are searching for the same thing as other microbes, namely, nutrients, in particular glucose. And what creates glucose in sake brewing? That’s right, the koji. At first, glucose, conversion happens slowly, too slowly at first and leaves the tank open to contamination. In order to speed up the conversion, the brewer pounds the mixture of steamed rice, water, and koji to increase contact between the starch and koji enzymes. This stage of making a kimoto shubo is called either motosuri or yamaoroshi. A specialized tool called a kaibo, which is basically a long wooden oar, is used. In order to limit unwanted microbial activity as much as possible, yamaoroshi is normally performed at very cold temperatures.

As the mixture is pureed and the glucose conversion is sped up, the lactic acid bacteria enter the tank. At first, the lactic acid bacteria is joined by other undesirable types of microbes and bacteria but over time it weeds them out and kills them. Once all the other bacteria have been eradicated and only the lactic acid bacteria remain, their job is done. For reasons not fully understood, the bacteria itself then dies. One theory is that the lactic acid they created is too strong even for them to survive. Whatever the reason, they have made the ultimate sacrifice.

This brewing method originated during the beginning of the Edo period meaning around the latter half of the 17th century.

Is the Yamaoroshi Really Necessary?

Traditionally, the yamaoroshi is carried out through the night into the early hours. So was this back-breaking work really necessary? It’s a question that went on unanswered for a long time. And then, in the early 20th century, a professor at a university in Tokyo, found the answer: It wasn’t. The professor discovered that if koji enzymes were dissolved in water first and this mixture called mizukoji (mizu is Japanese for water or liquid) was added before the steamed rice, there was no need for the yamaoroshi. In other words, the brewer simply has to switch the order that the ingredients are added. The water effectively acts as an alternative catalyst bringing the starch into contact with the enzymes. A little heat is sometimes required to activate the enzymes and the starch conversion process. Although this stripped down version of the kimoto removes a lot of the manual labor it doesn’t make the process any faster because the brewer still has to wait for the lactic acid bacteria to do its work.

The result is still the same as for the regular kimoto. This version of kimoto is called yamahai, which is an abbreviation for yamaoroshi-haishi (literally, omitting the yamaoroshi). All kimoto- made sake has a more rustic quality to it, higher acidity — in particular, lactic acid derived acidity — and in some cases, although not a dead cert, higher umami. In the case of regular kimoto, the extra lactic acid provides a sharp backbone to the sake with buttery, milky notes. Some people say kimoto tastes cleaner than sokujo, but a number of breweries purposefully create a funkier, wilder style of yamahai. They do this by exploiting the wild bacteria before they are eradicated, leaving them alive just long enough to produce the desired flavors. Sake in this style is quirky, with notes of mushroom, spice, chocolate, nuts, and game.

Commercial Grade Lactic Acid

It was not until after the end of World War II, that lactic acid was available to buy in liquid form. This is another reason sokujo came after kimoto and not the other way around. But liquid lactic acid removed the hassle of having to make lactic acid. The advantage of having lactic acid, to begin with, is that you can add the yeast a lot earlier. In the kimoto method, it is too risky to add yeast before the lactic acid bacteria has created lactic acid which can be as late as 14 days after starting the shubo. That is why while it takes only 14 days to make sokujo compared to the 30 days it takes to make kimoto. Another reason the kimoto process takes so long is that by keeping the temperature low for much longer to reduce the activity of undesirable microbes also slows down the desirable ones. The effect is that the entire process runs at a snail’s pace. But with sokujo, with all the unwanted bacteria eradicated from day one, the brewer can increase the temperature much earlier to speed up the process. There is even now a super version of sokujo which can be completed in half the time of sokujo, simply by increasing the temperature even more.

Which Method is Best?

Deciding which shubo method to use is a question of time, cost, practicality and flavor and aroma. Kimoto is a much more complicated process and requires a great amount of skill, so many breweries stick to sokujo. As well as skill, kimoto requires a room with a certain microbial balance. This is not something you can create overnight.

For many breweries, challenging kimoto is all about honoring the traditions of their ancestors. For others, it is the trademark of their style and part of their story.

By the end of the shubo, the sake already has an average abv of 8−10%.

Sometimes, the shubo method used to make the sake is printed on the label (sokujo is rarely printed on the label, but if nothing is printed on the label, chances are it’s a sokujo). Why not see if you can’t find the odd kimoto or yamahai or two the next time you are scanning the shelves of your local sake shop or menu of your favorite restaurant.

At KURAND, we always try to include at least one or two kimoto or yamahai in our 100 strong sake lineup, all available to taste at your own leisure, with no time limits, for just one flat fee. Each sake comes with a story of how it was made and no two sake are made 100% the same way. We look forward to welcoming you very soon! In this next article in this series, we will finally put all the ingredients together and explain how the sake is fermented.

Rice Preparation Stages: Recap

Koji Making Recap
Koji Making