Breaking up The Rice: The Second Step to Make Good Koji: Kirikaeshi

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 sake brewing process and offering even more insight into how they are carried out. In this article, we point the spotlight at koji-making/seigiku and lift the veil off the glorious detail of the process. In a previous article, we explained how the brewer kneads the rice to ensure that the rice receives an even covering of the koji mold. The second stage is breaking up or kirikaeshi in Japanese.

Article Glossary

Koji = steamed rice with mold growing on it
Koji mold = the mold used to make koji
Seigiku = process of making koji
Haze = pronounced “hah-zey”, describes the pattern of 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 centre of rice grain

Recap: What is Seigiku & Koji?


If you have read our previous articles about koji and the sake brewing process, you can probably skip this part of the article to the next heading: What is kirikaeshi.

After polishing, washing, soaking and steaming, the brewer will take a portion of the rice and turn it into koji. This process is called seigiku. The seigiku process is comprised of 6 distinct smaller stages: tokomomi, kirikaeshi, mori, naka-shigoto, shimai-shigoto, and dekoji. The process typically takes about 48 hours to complete, but this can vary by brewery according to their techniques and methods.

The purpose of koji is to break the starch down releasing glucose for the yeast to consume and create alcohol. This stage is necessary because just like in beer brewing, there is no available glucose in the raw ingredient, to begin with. This is the key difference from wine making that both beer and sake have in common. To elaborate further, koji is steamed rice with a mold of the same name inoculated onto it. This mold secretes enzymes that then cut up the chains of starch and reform them into glucose. It is important to note that as the rice is not germinated, it is technically incorrect to refer to this stage as malting or the finished koji as malted rice but for some people this does make it easier to digest, so we have used that term in the above flowchart. The reason the brewer cannot just germinate the rice in the same way that beer malt is made is that the germ which contains all the enzymes that break down the starch is removed in the polishing process. In other words, koji making is unique to sake.

As well as breaking up the starch into glucose, the koji breaks proteins down into amino acids giving the sake a richer flavor. Sometimes the koji also imparts a pleasant chestnut aroma. The quality of the koji will significantly affect the quality of the sake, so this is a make or break point in the brewing process. In the 1,2,3s of sake making, koji is number 1.

The latin name for the mold is Aspergillus Oryzae

The Inner Sanctum Where the Koji is Made

Because seigiku is growing and controlling the growth of mold, a specially designed room is required to maintain optimum levels of heat and moisture. This inner sanctum and sacred room of the brewery is called the koji muro. Many modern koji muro are connected to a switchboard where the brewer can monitor and control the temperature remotely. However, in the traditional koji muro, the brewer has to spend long hours in the room, which is not as easy as it sounds, given that the temperature can exceed 30 degrees with 80% humidity.

Koji-Muro Management

A sanitary environment is essential to ensure that the koji does not have to compete with any other microorganisms and bacteria. Lactic acid bacteria and the bacteria used to make natto (fermented soybeans) in particular are stronger than the koji mold, so throughout the brewing season, brewers have to abstain from these.

Before entering this sacred place, brewers must disinfect their hands, put on white coats, hats, and change footwear. It is rare to be allowed access to a koji muro so if a brewer ever offers this on a visit, think of it as a real privilege.

Most koji muro doors are built with a tight seal that blocks any cold air from seeping in. The brewer must also remember never to leave the door open. Good koji making is in the smaller details.

What is Kirikaeshi

So with that, we arrive at the main topic of this article, the second stage in seigiku, kirikaeshi.

Kirikaeshi is the process of breaking apart the rice grains. You are probably wondering why this would even be necessary in the first place. Following tokomomi, the brewer leaves the rice to stand 10-12 hours. During this time, as the mold grows and creates heat, the surface of the rice grains dry out and stick together. Just like other living organisms, the koji requires oxygen to grow. Therefore, the rice must be broken apart to give the koji access to oxygen. This is the primary purpose of kirikaeshi.

The temperature of the steamed rice that is clumped together is not uniform, and there is a risk that hot spots will appear. This will lead to uneven growth of the mold, and in the worst case scenario, some parts of the rice will overheat killing the mold. Another purpose of kirikaeshi is to even out the water content/humidity of the rice. Kirikaeshi is often repeated multiple times.

Kirikaeshi is Hard Work

Breaking apart steamed rice might sound like fun. However, you have to remember that the rice has solidified and is stuck together. Imagine having the task of breaking apart lego bricks at speed with your bare hands, and that’s what this job is like. The brewer must be careful not to damage the rice but must also complete this task quickly. It is unusual for a brewer not to build up a sweat during this task. Traditionally, brewers would strip down to the waist, but the idea of sweat dripping onto rice has led to a rethink in recent years.

Power of enzymes

Enzymes are a type of protein created inside the body of living things. There are two enzymes in sake brewing: amylase that breaks down starch into glucose and protease that breaks-down protein. So how vital is kirikaeshi? A bad kirikaeshi may lead to an immature koji mold growth, something called haze ochi. Kirikaeshi is such an important step; many brewers lose sleep keeping an eye it.

Quality Check: Hazekomi-guai

Haze is the Japanese word for the mold growth. Hazekomi-guai is the word for the state of the mold growth and is also an indicator of the quality of the koji. The toji or person in charge of the koji carefully checks the hazekomi-guai to determine the timing and temperature for the rest of the seigiku process.

Haze is measured as the number of koji mold that have extended their feeding tubes called hyphae deep into the rice. The two main types of haze are sou-haze and tsuki-haze.


Sou-haze is a covering of mold across the surface of the rice that has penetrated its hypha deep into the grains of rice.

The enzymatic power of this haze is perfect for a faster breakdown of starch and protein leading to richer sake with more body. Many junmai are made this way.

Tsuki-haze Koji

Tsuki-haze is a lighter covering of the surface of the rice grains and only some of the mold has penetrated the grains with their hypha, but where they have, the penetration is deep, in some cases into the shimpaku itself. It has enough enzymatic power to breakdown proteins, peptides, and starch, but the conversion is slower leading to far more elegant, smooth flavor profiles.

Many ginjo sake are made with tsuki-haze because the slower breakdown of starch and protein is perfect for putting the yeast under stress.


When the majority of the mold has failed to penetrate the interior, it is called nuri-haze.


The hypha has penetrated the core of the rice grain, but the enzyme activity has decomposed the structure causing it to become soft and brittle. Baka-haze koji crumbles apart when squashed between the fingers. Its enzymatic power is weak and leads to sake with heavier, more clumsy flavor profiles. Rice that is too soft—caused by too much moisture—is exceptionally prone to baka-haze and that’s why the earlier washing, soaking, and steaming stages play an understated role in the entire process.

Note: the degree of mold growth for each of the above hazekomi-guai can vary by brewery.

It is not enough for the koji-kin to naturally breed; the breeding must be stopped at the precisely the right hazekomi-guai for the style of sake being made. We hope that this article has offered more insight as to why this stage of sake making is often regarded as the most difficult—requiring the most skill—and the most important. Perhaps after reading this article, you have a better appreciation for the brewer’s craft, a lot of which is understated and goes under the radar of most drinkers (that’s not meant as a criticism; the ignorance is down to the modesty of brewing).

It is said that sake tastes even more delicious when you understand the effort that goes into making it.

In the next article, we will look at the third stage in seigiku, mori (mounding).

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.