Facts About Kimoto, The Traditional Yeast Starter Method

Greetings Sake Lovers

At some point during your sake journey, you are bound to come across the word kimoto, either as a style of sake or as some seemingly random jargon printed on the label somewhere. In Japanese, it looks like this: 生酛 or this き酛. But be careful not to get mixed up with the Japanese word for namazake which looks very similar: 生酒. Easier said than done after a few glasses of sake.

What is Kimoto?

This article will introduce a few facts about kimoto as well as explaining what it means.

The Traditional Method of Yeast Starter

Similar to some types of strong strength beer, sake uses a yeast starter, a smaller fermentation which forms the base for the main fermentation. Why the need for a starter you might ask. The tank that sake is fermented in is open (lidless), an open door to wild bacteria from outside. In order to keep these bacteria from coming in and spoiling the sake, the brewer must grow the yeast into a big enough population to be able to defend itself (a large population is also required to drive the fermentation). Yeast is tolerant to high acidity but wild bacteria is not so this is the key. The logic behind using a starter is the same as building a campfire. If you put the big logs on first before the fire is able to kindle, it suffocates and goes out. Similarly throwing all the ingredients into a big tank with the yeast overwhelms it and stunts its growth. That is why brewers use a smaller version. Although this article doesn’t cover the rest of the production process in that much detail, the name for the starter in Japanese is shubo and moromi for the main fermentation.

As explained, the starter is essentially just a smaller version of the main fermentation so the ingredients are the same:
steamed rice, malted rice, and water.

The key question is how does the brewer increase the acidity. In modern brewing, the answer is lactic acid. Hundreds of years ago, when the science behind brewing sake was still very much a mystery, through trial and error and a bit of luck, brewers discovered a starter method that borrows the help of lactic acid bacteria in the air. They begin to enter the tank when there are enough nutrients in the starter. Nutrients are created by converting the starch in the rice into glucose by the action of the koji. Lactic acid bacteria then produces lactic acid which, just as in modern brewing, raises the acidity level killing off all the unwanted bacteria. It is only when all the bacteria is dead that the yeast can then grow inhibited. The modern method is called sokujomoto (the quick method) and the old one is called kimoto.

Making Kimoto Requires Hard Work

Kimoto is much more labour intensive. The brewer has to create the starter at a low temperature to avoid the growth of unwanted bacteria, but this also slows the rate of conversion of starch into sugar and without sugar there is no yeast growth. The alternative is to purée the mixture of koji and steamed rice to forcefully put the koji enzymes in contact with starch. The brewer transfers the mixture into small wooden buckets and pounds it with wooden oars until it is a porridge mixture. The technique is called yamaoroshi (literally, knocking the mountains down) so-called because of the way the brewer piles up the mixture before ramming it. The process is divided into 3 4 hours shifts. It is very labour intensive and takes 2 weeks longer to complete than the modern sokujo method with more risk of contamination. The rate of pureeing has to be uniform so many brewers sing a song to keep in rhythm with each other.

As the texture thickens, the lactic acid bacteria starts producing lactic acid raising the acidity beyond the point that wild bacteria can survive. In fact, even the lactic acid bacteria itself eventually dies. Exactly what kills off it is still a bit of a mystery. But by this time it has fulfilled its role so its sacrifice is not in vain.

Kimoto is often carried out in the middle of the night, often continuing into early morning hours which in the winter is really hard work.

In short, kimoto is a traditional method of sake brewing that uses the power of natural lactic acid bacteria!

Replacement of Yamaoroshi: Yamahai

Around 1920, a scientist succeeded in making kimoto without yamaoroshi by dissolving the ingredients in hot water.
They discovered that the starch comes into closer contact with the koji enzymes in water and heat speeds up the dissolving of the starch into the water.

The process was named yamahai which is short for yamaoroshi haishi (literally, omitting yamaoroshi).

The Flavor of Kimoto Sake

Sake made with the kimoto method is more bold and pairs really well with the sort of rich, oily dishes that other styles struggle to get on with. Kimoto sake tends to be much more acidic. Yamahai often has wild gamey flavours which are produced by the wild bacteria before it is killed off.

Thanks to the more robust character and clear finish, kimoto is a great sake for serving warm.

At KURAND, we often showcase one or two kimoto and even the odd yamahai among the 100 different types of sake in our fridge. Why not come to KURAND and continue your sake journey the next time you are in Tokyo. We look forward to welcoming you.