Next year will mark the 60th anniversary of the discovery of perhaps the most important saké-brewing yeast strain of all, the Kumamoto yeast, also known as “Yeast Number Nine”. While the yeast itself, its qualities, and its various aliases are worth knowing about, the history and culture surrounding all this is interesting as well. It all took place down south in Kumamoto Prefecture, thanks to the efforts of a man named Professor Kin’ichi Nojiro. This family of yeast is very suited to making aromatic, yet clean ginjo-shu. And today, more of that kind of fine saké is being produced then ever before. This leads to great demand for the #9 strains. So what some prefectures do (most notably Yamagata, but other places as well) to make it more accessible is to buy some Kumamoto Kobo from the source, then propagate and distribute it amongst those that want it in that prefecture. This is significant only because amongst Yamagata saké, one can find a yeast called Yamagata KA, which is Yamagata home-grown Kumamoto Kobo.
So what is so special about it? In brewing, it ferments thoroughly and slowly at low temperatures, allowing brewers to control the fermentation closely. This all leads to wonderfully smooth and fine-grained flavors, good aromatic acid content, and lovely fruity aromas reminiscent of delicious apples and perhaps melon. Clean and bright saké with wonderful balance is the trademark of this line of yeasts. Indeed, there is nothing quite like classic #9 flavors and aromas in a saké. These days especially, there are many other great yeasts. Whether or not they will still be great in 50 years is yet to be seen. And it is certainly possible to enjoy your saké without giving a hoot about the yeast used. But often, the more one tastes, the more one wants to know why certain sakés have the aromas and flavors they do, to know what makes a saké the way it is. Should your interest get to that level, remember ole’ Number Nine.