Learn about Yeast No. 9 and Its Importance in Ginjo Making15 Nov 2018
Yeast is unarguably one of the most important ingredients in sake brewing. To summarize the sake brewing process very briefly, starch in rice grains is converted to glucose by koji while the glucose is converted to alcohol and carbon hydrate by yeasts (simultaneous fermentation). Thus yeast, or kobo (酵母) in Japanese, needs to stay active throughout the moromi (mash) fermentation process. In general, yeasts tend to produce good aromas when exposed to hard conditions. However, if unable to withstand the hard conditions, they may produce undesirable flavors and aromas, or stop fermenting. Accordingly, a variety of yeasts are distributed from Japan Brewery Association, originally collected from the moromi of sake breweries all over Japan. This collection of yeasts is distributed by an association which is known in Japan as Kyokai Kobo (きょうかい酵母).
There are many different yeasts and they are usually called by their number (No 7, No. 9, etc.). You might be wondering why there is a necessity for such a variety of yeasts.
During the alcoholic fermentation, yeast produces by-products such as acid, amino acid, aroma components (esters) and the like which all have substantial effects to the aroma and the flavor of the final product. The nature of those by-products is different depending on the types of yeasts. Also, the temperature at which they are most active varies with the types of yeasts. Therefore, sake breweries decide which type of yeast to use depending on the brewing method and the sake they wish to produce.
No. 9 is the most common yeast used in ginjo sake. In fact, it is used for ginjo by so many breweries that it is sometimes called "the base of modern ginjo sake". No. 9 gives ginjoshu that fuity aroma which is enjoyed so much by ginjoshu fans around the world.
This yeast, also known Kumamoto Kobo, was isolated around 1953 by Nojiro Kinichi at the Kumamoto Prefectural Brewing Research Centre (Kumamoto Shuzo Kenkyusho).
Let us explain what is so special about it. In brewing, it ferments thoroughly and slowly at low temperatures, allowing brewers to control the fermentation closely. This results in wonderfully smooth and elegant flavors, good aromatic acid content, and fine fruity aromas reminiscent of apple and melon. Well balanced, clean and bright sake is the trademark of this yeast strain. There is nothing quite like classic No. 9 flavors and aromas in a sake.
Kumamoto Shuzo Kenkyusho is well-known for developing number 9 yeast but they are more that that. They are also makers of extremely high-quality sake brand known as ‘Koro’.
In general, sake from Kyushu is more bitter and acidic compared to sake from other regions. However, Koro Junmai Ginjo is not your typical Kyushu sake. It has a very rich flavor that spreads in your mouth. The number 9 yeast gives this sake a unique flavor; slightly fruity, with a hint of strawberries.
We invite you to try the finest quality sake from the brewery which created Yeast No.9!