An Often Overlooked Ingredient of Modern Sake: Yeast – Kyokai No.7 (Masumi Yeast)

Greetings Sake Lovers!

Welcome to another article introducing little nuggets of sake knowledge. The rice is undoubtedly one of the more talked about ingredients in sake making, it is after all the main ingredient. But one other important ingredient that doesn’t get as much attention is the yeast. Which is a bit of an injustice considering that alcohol fermentation is not even possible without it.

Nowadays, brewers have a number of proprietary yeast to choose from.
The current industry standard is called Kyokai No.7 and it is this that we will be looking at in this article.

The Evolution of the Sake Yeast

In sake brewing there is an old saying: First, koji; second, moto (yeast starter); third, moromi (mash / main fermentation). In other words, the yeast is the key ingredient in the second most important stage of brewing. (see these past articles about moto or shubo as it is also called).

The Japanese word for yeast is kobo. Brewers originally used ambient, naturally occurring wild yeast living inside the brewery environment; on the walls, in the air, even on the equipment. This yeast was unpredictable though and produced unreliable, inconsistent results: varying aroma, acidity, fermentation vigor and stability, etc. By the early 1900s, thanks to advances in science and technology brewers had become able to isolate particular wild yeast from successful fermentation batches and breed them in the laboratory.

Ever since the early 1900s, these yeasts have been distributed by the Brewing Society of Japan. These proprietary yeast which are available for brewers to purchase are aptly called Kyokai Kobo (society yeast). There are over 20 varieties, each discovered at a different brewery in Japan. For the breweries that discovered them, the yeast have earned them fame throughout the industry. New yeast are still being discovered and the society’s scientists are always on the lookout for clues which might lead to the next eureka moment. A new discovery normally happens by tracing new interesting flavors or aromas back to the brewery and narrowing the source down to the yeast they are using. Suffice to say, these so-called eureka moments don’t happen every day, but sometimes wild yeast finds its way into the sake and leaves a little calling card.

Instead of naming the yeast after the brewery, the yeast are given numbers such as No.3, No.4 No.7, etc and abbreviated to Kyokai and the number or even just the number.

The society discovered Kyokai No. 7 at Nagano prefecture at a brewery called Miyasaka Jouzou, which makes the brand: Masumi. Some people refer to it as the Masumi Kobo, but even the brewery prefers to refer to it as just No.7.

The Story Behind the Discovery and Development of Kyokai No.7

The main purpose of the early Kyokai Kobo such as No.1, discovered in Sakuramasamune, Kobe and the 4 yeast that followed was reliable, stable yeast that reduced the number of failed batches, a big problem in the early days of brewing. But by the mid 1900s, there was demand for yeast that could influence the final sake style. The breakthrough discovery came with Kyokai No.7.

Masumi explains more on their homepage:
“In 1946, Masumi swept the top awards at the regional and national sake appraisals, which got the attention of the brewing institute’s yeast scientist, Dr. Shoichi Yamada. Dr. Yamada visited us and confirmed the presence of a very fine yeast in the fermentation tanks. “Brewing Association Yeast Number Seven” soon became the favorite of brewers across the nation and remains even today the most widely used sake yeast in the world.”

The characteristic in Masumi sake that had caught the attention of the scientist was an aroma profile called a ginjo aroma, so-called because it is more commonly found in ginjo sake. More about ginjo here. A ginjo aroma is a gorgeous fruity / floral aroma; aromas of banana, melon and white flowers. Scientists realized that somewhere in Masumi’s brewery there was a yeast producing these aromas.

Was it just luck that this had chosen to appear in Miyasaka Jozo?

“While number seven was originally our “house” yeast, it cannot be said that our president at the time, Masaru Miyasaka, or his master brewer Chisato Kubota “developed” this yeast. Rather, their insistence on keeping the brewery clean provided the right environment for fine yeast to thrive.”

In other words, luck might have played a small part, but Masumi had provided the right environment for the yeast to thrive in the first place.

Characteristics of Kyokai No.7

Over time, the gorgeous ginjo aroma of Kyokai No.7 has mellowed and now produces more balanced flavour profiles. This balance which produces sake with a more mature taste is the reason that Kyokai No.7 is now the industry standard. Often referred to as the yokozuna of sake yeast, breweries up and down the country use Kyokai No.7 to produce not only ginjo, but inexpensive sake. One of the great things about Kyokai No.7 is its vigor; a vigor that is essential for a fast fermentation, which is essential to yield high volumes. But what sets inexpensive sake made with this yeast apart is the mild fruity, floral aroma.

Many people assume that Masumi benefited financially from this discovery, but as the brewery explains that is not necessarily the case:

“In fact, we have no patent for it and do not sell it. Even so, it is still a great honor to be among the few sake makers that gave birth to a numbered yeast. Of course, this also gives us greater incentive to live up to that honor by continuing to produce exceptional sake”.

A modest statement that makes their story all the more inspirational.

It is not so common for breweries to denote the yeast variety on the sake label, so it can be a little tricky to locate sake made with particular varieties. That said, so many breweries use Kyokai No.7, that the probability of tasting a sake made with it is very high. At KURAND, with over 100 types to choose from in our all-you-can-taste extravaganza, this probability is greatly increased. Sometimes we do showcase sake that clearly list No.7 as one of the ingredients. It is also possible to taste in wine glasses which allow these type of sake to better express itself. Why not pop by the next time you are in Tokyo, and discover sake the KURAND way. Sometimes you can even meet the brewers themselves. We look forward to welcoming you soon.