Best While Stressed: Yeast
We enter the final chapter of our sake ingredient series – Yeast.
Simply put, yeast is a microorganism responsible for digesting sugars, converting them into carbon dioxide and alcohol during fermentation. As previously covered, without koji (mould-inoculated rice), there would be no sugar to work with, and without yeast, there would be no alcohol. This would be rather impractical in the world of sake. Working together, these essential microscopic ingredients conduct 'multiple parallel fermentation,' gradually transforming steamed rice into the fabulous beverage we all know and love (with a little help along the way).
Where Do Brewers Get It?
Not to alarm you, but yeast is almost everywhere – from particles floating in the air to those residing on fruit surfaces and even human skin. With an almost infinite source, brewers traditionally relied on these wild ambient yeasts, which would land in and naturally inoculate the sake mash. Even nowadays, some brewers are returning to natural yeast sources – from flowers to local plants.
Our Hachi Hachi is a perfect example of sake produced with yeasts derived in this manner – Shodoshima Brewery President Aki Ikeda commissioned the development of Sanuki Olive Yeast No. 23, a strain derived from the famous olives of Shodoshima Island. This yeast strain was used to brew Hachi Hachi, a unique sake with expressive notes of citrus, minerality and a hint of olive brine.
In modern sake production, brewers typically use cultivated yeasts to ensure consistency and control over the final product. The Brewing Society of Japan distributes various yeast strains, each with specific characteristics. Our Iwate Homare Junmai Ginjo uses Association Yeast No.6, the oldest cultivated yeast offered by The Brewing Society today. What it lacks in aromatic intensity, it makes up for in juicy acidity. As you can see, these yeasts are often referred to by numbers, even diversifying in further years to designate between 'foaming' and 'non-foaming' versions. The less foam produced by the yeast leads to higher space efficiency during brewing, with less chance of bubbly overflow.
Cheat sheet: if a yeast strain has '01' at the end of the number, it is the non-foamy version of its counterpart.
More Stress = More Flavour:
Different strains of yeast are responsible for producing enticing aromas, such as pronounced notes of green apple, pineapple and banana, which you can detect on the nose of a good glass of ginjo. Over time, brewers discovered a new and efficient technique for unlocking this aroma: stressing out the yeast.
Rather than poking and yelling at the fermentation mash, brewers found that limiting yeast's access to food (sugar) and keeping the brewing temperatures low would do the trick. In turn, the yeast would voice its displeasure by releasing esters – compounds responsible for distinguished, fruity aromas. Yum!
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If you’re interested to try any yeast-focused sake from our collection, take a look at our:
Hachi Hachi - as previously covered, using specially commissioned Sanuki Olive Yeast No. 23
Iwate Homare Junmai Ginjo - using Yeast No.6, the oldest strain of cultivated yeast from The Brewing Society of Japan
Sparkling Rosé - with a special strain of yeast to thank for its pink tint
White Eikun - solely using terroir-driven ingredients, including the Shizuoka Yeast NEW-5, leads to a fully Shizuoka-based brew with lightly sweet notes and a clean finish
In conclusion, yeast is a critical component in sake brewing, contributing up to 60% of the flavours and aromas found in the final product (according to researchers at the Kyoto Municipal Institute of Industrial Technology and Culture). From traditional wild fermentations to carefully selected cultivated strains, the choice of yeast profoundly influences the character of sake, meaning we'd be nowhere without it.
