Innovation must be in the water

Hiroshima is famous in the sake world for two things: incredibly soft water and figuring out to brew with it, a low-temperature technique developed by local hero Senzaburo Miura which eventually evolved into what we know today as ginjō style brewing. (While his friend Ryuichi Satake worked on powered rice polishing machines.)

And the drive to keep on finding ways to make the best sake continues with Imada Miho, kuramoto-tōji at Imada Shuzō in the nearby seaside town of Akitsu. She has had an eye on overseas markets for some time, and exports now account for 30% of her brewery’s sales.

Exporting means long periods in storage and transport, and people handling the sake who may not know how to keep it in top condition. But rather than tackle the problem after the sake leaves the brewery, the Hiroshima Prefecture Food Industry Technology Center bred a new sake yeast designed to minimise the risk of deterioration during transport and storage.

The new yeast was codenamed A1-1 during development and released in January 2025 as Hiroshima LeG-Sou (LeG-爽, spelled out as レグソウ, legu-sō, meant to sound like the word “legacy”, with the letter G standing for the number 6), It was bred from the now unused Hiroshima No. 6 sake yeast, taken from Kikubotan Shuzo during the Taisho Period and coincidentally the first yeast isolated in the prefecture.

The Hiroshima Prefecture Food Industry Technology Center describes Hiroshima No. 6 yeast as closely related to the current range of Kyokai (Association) yeasts, but with genetics that work to suppress deterioration of aroma in storage. It is also amenable to cross-breeding as unlike most yeast it readily forms spores. This led the centre to invent a new technique where rare spores from Kyokai-related yeast were crossed with Hiroshima No. 6 yeast to produce new strains, without the need for other means of generating variety such as forced mutation.

The new hybrid strains were tested in small batches with Yamada Nishiki polished to 35%, and actually outfermented the known Hiroshima ginjo yeast strain they were benchmarked against. Sake made with the new strains stored for 3 months at 45°C had undetectable levels of DMTS, and significantly lower levels of sulphur aroma than a control.

The new yeast produces refreshing malic acidity and plenty of isoamyl acetate, and is used by Imada Shuzo in their Seafood and Bon Time Style:B sake, by Enoki Shuzo in their Kijoshu Nouveau, and by Hakubotan in their Renka Rouge and Mitaniharu tokubetsu junmai.

Mitaniharu won Platinum at the Singapore Sake Challenge, proving that being bred to produce less components liable to deteriorate hasn’t harmed the yeast’s ability to make great sake. It will be available from the Hiroshima Prefecture Sake Brewers Association.

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輸出用清酒の醸造に適した品質を向上させる酵母開発 (Hiroshima Prefecture site, 24 Jan 2025)
新規の育種法導入による輸出用清酒の品質向上に寄与する清酒酵母の開発 (Hiroshima Prefecture food Industry Technology Center, not dated)
“Sake’s export boom bringing in new fans and food pairings” (Kyodo News, 28 Apr 2025)
“Saijo – Sake Theme Park” (Sake Deep Dive [Spotify] [Apple Podcasts], 1 Sep 2023)