Why knead the rice? The first step to making good koji: Tokomomi

The world of Japanese sake is profound; the process of how it is made and the resulting end flavour difficult and complex. But it’s precisely this complexity that sets the bar for Japanese sake so high and creates a world that once you step foot in, you never want to leave.

In this article, we will take a look at one of the most important stages of the production process: “tokomomi.” Very few people will have heard of this, let alone know that this is one of the stages of sake production, but they might have heard of the process that it is a part of that we covered in the previous article: “koji making”.

What is koji making?

Before we dive into an explanation about “tokomomi,” let us first review what “koji making” is. After a batch of polished rice has been washed, soaked and steamed, the rice goes through the process of “koji making” or “malting”.

Malting is a stage that is also present in beer production because like sake, beer is made with an ingredient that is absent of the key ingredient required to produce alcohol: sugar, but it does contain starch.

Starch is basically sugar, packaged in a way that creates a space-efficient energy store. This package can be broken down into sugar (glucose) by enzymes. The “koji making” process is divided into 6 sub-stages: tokomomi, kirikaeshi, mori, nakashigoto, shimaishigoto and dekoji.

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Koji is both the name for the malting process and it is also the name for the little fella that produces the starch-degrading enzymes. Known by the latin name, Aspergillus Oryzae, Koji is actually a type of mold. After transporting or carrying the steamed rice into the Koji room, the brewer sprinkles seed malt of this mold onto the rice. The koji has two roles: to saccharify (convert starch to sugar) the rice (as explained above) and also to help add body and depth to the end flavour. Suffice to say, making good koji is an essential part of sake brewing and the key factor in deciding the quality of the sake created.

The 1,2,3s of sake brewing

No saying stresses this importance better than the 12,3s of sake brewing: “1. Koji, 2.Moto (yeast starter), 3. Fermentation”, a brewing code that all brewers swear by.

“Kojimuro” (room for making koji) the place where koji making takes place

The art of making good koji is all about perfect temperature control. This is the reason why koji making takes place in a special temperature controlled room called a “kojimuro.” It resembles a Swedish sauna and feels like one with the interior temperature set at roughly 30 degrees Celsius. Working in this environment is a lot harder then it sounds.

Necessary steps for koji making

Kojimuro have to be kept as clean as possible so that no dirt or bacteria besides the koji mold interferes with the koji’s growth. The bacteria used to make Natto (fermented bean paste) in particular is much stronger than Koji and so it is normally absent from the brewer’s table throughout the brewing season, just one of the restrictions they have to endure. Before entering the kojimuro brewers disinfect their hands, change or remove footwear, and change into white uniforms and put on hats.
 The kojimuro is often structured so that it is wind proof. Even when going in or out, great care is taken to make sure the door does not remain open. These small attentions to detail are the key to good koji.

What is tokomomi?

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The objective of the first stage of Koji making, “Tokomomi” is the process of sprinkling the seed malt on the steamed rice and kneading and mixing it so that the rice gets an even covering. The Toko is the name given to the large bed where this takes place.

Before “tokomomi,” the steamed rice is spread out inside the kojimuro in a process called “hikikomi” (lit: bringing in) and left for 2-3 hours to calibrate the end product. When the temperature of the steamed rice has lowered to around 32-35, the seed malt nicknamed, “moyashi” is passed through a sieve and sprinkled onto the rice in a process called “tanekiri”.

After the koji mold is spread evenly throughout the rice, the rice is broken up, kneaded and mixed repeatedly by hand. This is to enable the koji mold to breed effectively and consistently, the rice is then gathered up into a mound and covered with a cloth.

The stage is summarized below:

[Hikikomi] Spreading steamed rice in the kojimuro, on the Toko and letting it cool
[Tanekiri] Sprinkling the seed malt on the rice
[Tokomomi] Breaking up, kneading and mixing the rice
“Tokomomi” sounds easy but it requires highly advanced skills.

What is the Seed Malt?

The seed malt used to make Japanese sake is basically brown rice inoculated with the spores of koji mold. There are 3 main types of koji mold: yellow koji mold, black koji mold and white koji mold. White and black are more commonly used to make Japan’s indigenous spirit, shochu. They really contain too much citric acid to be suitable for sake production although some breweries have started to experiment.

The yellow koji mold that is used in Japanese sake is highly effective at degrading starch. For this reason, Japanese sake can be brewed even in the colder seasons while keeping the number of wild bacteria low. Sake can also be fermented at a low temperature because this type of ferment produces enough heat to keep the yeast alive (yeast normally does not like cold temperatures) even though the extra stress causes it to become less active. But stressing the yeast out in this way is how brewers produce sake with far less zatsumi (unfavorable taste) in more smooth, delicate styles.

Why is it Nicknamed Moyashi?

Koji is not just an essential ingredient in sake, but in nearly all of Japan’s fermented ingredients which make up 80-90% of Japanese cuisine and include: soy sauce and miso, etc. In all the production of all fermented products that use the power of koji, the seed malt is referred to as Moyashi. In fact the factories are even sometimes nicknamed as Moyashi-ya (Moyashi houses).

But why “moyashi?“

Simple: because the mold shoots out little Hypha (legs) that resemble the strands of Moyashi which is the Japanese for beansprouts.

Temperature is Key

The temperature setting during Tokomomi is called the Momiage Ondo (lit: kneading temperature) and depends on the style of sake being made but it is generally somewhere between 32-37 degrees Celsius. The more the koji mold is able to breed, the more starch conversion there will be which produces a richer, heavier sake. Sometimes this is desirable and sometimes it is not. Whatever the style, it is necessary to keep the koji mold in an environment where the temperature is kept at a level which is ideal for breeding and where it will not dry out.

The momiage temperature will determine the speed that koji mold breeds so it is extremely important to manage the temperature during the momiage after the tokomomi.
In the next article, we will introduce “kirikaeshi,” the process of breaking apart the rice that has turned into hard blocks as a result of tokomomi!