Kimoto and yamahai styles of sake seem to have something of a cult status among sake fans. This may be attributable to the fact that they are somewhat rare, or perhaps that so few people actually know what they are and what makes them special. But that veil of mystery is not necessary; you can lift it with minimal background information. These two types are in fact fairly similar from a production standpoint.
First, let’s look at the basics. Kimoto and yamahai refer to traditional production methods, and the terms are mutually exclusive of grade. They could apply to futsû-shu, a junmai-shu, or even a daiginjô. Next, both terms refer to methods of preparing the yeast starter that usually lead to a wilder, gamier sake. Third, even though they are attracting increasingly more attention, very little sake is made using these methods. Most sake is not kimoto or yamahai. The very least that you need to remember is this: kimoto and yamahai refer to methods of preparing the yeast starter that usually lead to wilder sake.
Taking a step back, when sake is made the first milestone is a small tank of ingredients that begins fermenting, the goal of which is a yeast starter with a very high population of yeast. Yes, alcohol will also be produced during this fermentation, but the real goal is yeast cell reproduction. The product at this stage is interchangeably called a moto or a shubo.
Why is such a high yeast population sought? Because sake is made using an open fermentation–there is no lid on the tank. This means that every offending wild yeast strain and other microorganisms can and do drop in to the tank. There needs to be a lot of ‘good’ yeast cells to ensure the sake is not affected by any wild yeast. This will also maintain a vigorous fermentation, which will blow off a lot of carbon dioxide, further protecting the fermenting mash.
The aforementioned ingredients that go into the moto are rice, water and kôji. Also, for almost all sake made, a small amount of pure but industrially created lactic acid is introduced to clean out the environment, after which cultured yeast will be added.
The lactic acid kills off almost everything, and by a miracle of nature, sake yeast actually likes a lactic environment. However, it is not necessary to use industrially produced, pure lactic acid. The moto can also get that lactic acid from another source: lactic bacteria that are floating around in the air.
This is how kimoto and yamahai are different from most other sake. Both of these methods utilize lactic bacteria from the environment. The bacteria create the lactic acid needed to clean out the inside of the moto so that sake yeast cells can divide and multiply.
In summary, kimoto and yamahai moto are created with rice, water and kôji, whereas all the rest (easily 99% of what is made) is made with rice, water, kôji and a dose of lactic acid. That is it in a nutshell.
So what’s the big deal? Who cares where the lactic acid comes from? It matters because these two styles taste significantly different from “regular” sake. Kimoto and yamahai are, in general, wilder and gamier. Acidity, sweetness, and umami are often–but not always–more prominent.
And–important to this article–this applies to yamahai more than it does to kimoto. Yamahai is very often wilder and gamier, sometimes rambunctiously so. Kimoto is surely more pronounced in these ways than regular sake, but typically kimoto comes across as slightly and pleasantly tart, with a very finely grained texture, rather than being gamey or wild. Why is this? It seems no one is really sure, but we’ll come back to that in a moment.
Let us have a look at the differences between kimoto and yamahai. We know they share the technique of using naturally occurring lactic bacteria to get their lactic acid. Kimoto, however, has been around much longer–for hundreds of years, in fact. Yamahai was developed around 1910 by a researcher named Kin’ichiro Kagi at the Suehiro brewery in Fukushima. Of course, the actual methods are more significant than the history.
Kimoto is made by taking the small tank of ingredients and splitting it up into about eight even smaller, shallow vats. Brewery staff then use poles to mix and mash the rice and kôji into a puree. They do this several times a day for the first few days. It can be tiring and hasslesome work. However, the enzymes required to liquefy the rice are in fact available, having been produced by the kôji. This means that the hard work of physically liquefying it should not be necessary. So they learned to adjust temperature and moisture within the little mash to maximize the ability of those enzymes to liquefy the rice. And it worked.
Yamahai eschews the laborious pole ramming, instead using moisture and temperature variations to achieve the same thing–dissolution of the rice and kôji. Since brewery staff do not need to do the pole ramming, the moto is not divided up into little vats, either. It all stays together in a medium-sized tank. While there is a bit more to it, it’s not much more. That’s the gist. The big differences are only in the first few days.
Why are they different from each other? If that is all that differs between them, why does yamahai taste so much gamier than kimoto? Again, no one knows for sure. Some speculate that because a yamahai yeast starter stays together in a slightly larger tank, a whole host of wild yeast and other microorganisms are able to live, die and subsequently decompose in the yamahai tank, which is not possible when the moto is split up into a handful of comparatively smaller vessels for mixing. Even though this stage takes but a day or two, the result is evident.
Also, keep in mind that kimoto and yamahai do not mean naturally occurring yeast. With just a very few exceptions, cultured yeast is added for all sake as this promotes consistency and lets a brewer potentially control other things, like aromas, acidity and robustness of fermentation. Please be aware of that misperception; remember that kimoto and yamahai mean naturally occurring lactic bacteria, not yeast.
Having said that, sake can be made without adding yeast; it will drop in from the air when the conditions are right. And in fact those conditions can only exist if the production is yamahai or kimoto. So while these terms do not mean naturally occurring yeast, if a sake is going to be made that way, it must be one of these two methods. Either way, very, very few sake are made using wild yeast anymore.
Kimoto and yamahai have a lot in common, as you can see. They have more notable differences in the way they typically unfold in your glass. Again, just why that is, no one really knows for sure. Welcome to the sake world. Enjoy tasting the difference.
