Celebrating #6

First of all, a quick recap on the oldest lines of sake yeast – after scientific investigation of what happens during sake brewing started in the early 1900s, an organisation that would later become the National Research Institute of Brewing (NRIB, Shurui Sogo Kenkyujo, 酒類総合研究所) took yeast samples from successful sake breweries around the country and entrusted them to what would become the Brewing Society of Japan (BSJ, Nihon Jozo Kyokai, 日本醸造協会). These sampled yeast strains are now known as Kyokai yeast and identified by a number given sequentially in the order in which they were isolated.

Banner from the National #6 Yeast Summit closing session.
(Kikkawa Instagram)

Many of the oldest yeast strains have dropped out of mainstream use (although both Tamagawa on the coast of Kyoto Prefecture and Sakura Masamune in Nada, Hyogo Prefecture, are currently brewing with the #1 yeast isolated from the latter brewery in 1906) but several are still popular today–including #6 which was isolated from the Aramasa brewery in Akita Prefecture in 1930.

#6 is now the oldest yeast actively distributed by the BSJ, which is something to celebrate in and of itself, but there is also an annual National #6 Yeast Summit held since 2016 in June (month 6) where brewers using this most classic yeast come together to exchange news and views, listen to speakers and–most importantly–enjoy sake made with #6.

The Aramasa site has an interesting take on the early sake yeast and where they were isolated–namely that this acts as a snapshot of the rise and fall of brewing areas over time. #1 came from Nada, then #2 from Gekkeikan in Fushimi, Kyoto. However, Nada and Fushimi faced a new challenger in the Taisho Period (1912–1926) in the form of Hiroshima, which had previously struggled due to its extremely soft water. Kyokai Yeast #3 was isolated from the Suishin Brewery in Mihara near the Hiroshima Prefecture coast, #4 from an unknown brewery in Hiroshima, and #5 from Kamotsuru in Saijo. The Aramasa site sees this as evidence of the dominance of Western Japan over sake brewing, stemming from the fact that the earliest organised brewing happened in the ancient capitals of Nara and Kyoto.

The key characteristic of #6 yeast, which went on sale in 1935, was that it fermented reliably in cold temperatures, down to under 10°C. This gave an edge to brewers in the colder climates of the Tohoku, Hokuriku and Shinshu regions which are all recognised today as important sake brewing areas.

The timing of the isolation and sale of #6, combined with yeasts #1–5 falling out of favour soon after it became popular, also meant it was the only yeast on sale during WWII. This is probably why it is only weakly genetically related to yeasts #1–5, but many yeasts that emerged after #6 are close genetic relatives–so, you could say #6 is the mother of many modern yeasts.

The 2025 summit was hosted by Taro Kumagai, owner of the La Jomon brewery, and held at the Auberge The Takinami in Yamagata Prefecture. Attendees included Yusuke Sato of Aramasa (Akita Pref), Naoaki Kuribayashi of Kuribayashi (Akita Pref, makers of Harukasumi), Aoki Risa of Aoi (Niigata Pref, makers of Choryo), Norimichi Goto of Kikkawa (Kanagawa Pref, makers of Afuri) and Shoya Imai of LINNÉ (Kyoto Pref, former toji at Wakaze Paris). Previous events have attracted 150–300 guests.

La Jomon released a special limited edition sake for the event, a mizumoto wine kijoshu made with Kame no O rice, with part of the brewing water replaced with wine made with #6 sake yeast, aged at -5°C for six years.
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６号酵母サミット@山形座 瀧波 Kikkawa Instagram post (14 May 2025, Japanese)
6/9【全国6号酵母サミット with 吉田類】が開催！ Sakagura Press (8 June 2017, Japanese)
水酛ワイン貴醸酒仕込み「阿字観」 Big Advance (1 May 2025, Japanese)
About La Jomon site (accessed 9 June 2025, Japanese)
History Aramasa site (accessed 9 June 2025, Japanese)