Today, I would like to talk about Sake yeast. The yeast makes alcohol from sugar which is converted from starch of rice by Koji enzymes, and creates origanic compounds. Also, the yeast is the important factor to create the aroma and flavour compunds and determine the style of Sake. Different yeast strain creates differrent aromas.
Traditionally, the brewers used "ambient yeast (wild yeast)" which is attached on the surfaces in the berwery. As the science is improved, the brewers started to select and picked up the yeast from the foam of the tank which has succesfull fermentation, and inoculated the next fermentation. As the science is imporeved further, they isolated the individual yeast strains so that they achieved the consistency of Sake brewing. Today all of brewery ues yeast strains which is storaged and multipled by Brewing Society of Japan.
Brewing Society of Japan
Brewing Society of Japan manages multiplication of yeast and keeps the characteristics of the strains. Furthermore, they offers information on brewing technology through research and investigation. They also publish thier monthly bulletin.
The yeats which are kept by Brewing Society of Japan is called Brewing Society yeasts, and they are registered by the number. Almost yeast was isolated by a particular brewery. Today, some new yeasts are developed. No. 1 yeast to No.5 yeast are isolated from some breweries, but, currently, they are not supplied.
No.6 yeast (Aramasa yeast)
This yeast is isolated from Aramasa Brewery "Aramasa (brand name)" in Akita prefecture. This yeast ferment extremely reliably and strongly. The Sake uses this yeast tends to be gentle and clear aroma and clean taste, and have more acidity than morden yeast.
No.7 yeast (Masumi yeast)
This yeast is isolated from Miyasaka Brewery "Masumi (brand name)" in Nagano prefecture. This yeast ferment extremely reliably and strongly like No.6 yeast, and has more acidity than morden yeast. This is widely used in Japan as industrial standard yeast, because this yeast is generally felt to be slightly more attractive (sweeter and furitier) than No. 6 yeast. No. 7 yeast is used for both normal (basic) Sake and premium Sake (Honjozo, Junmai and also Ginjo).
No.9 yeast (Kumamoto yeast, Koro yeast)
This yeast is isolated from Kumamotoken Shuzokenkyusho "Koro (barnd name)" in Kumaoto prefecture. This is suitable for Ginjo brewing, pursuit of better aromas. This yeast produces a higher level of acidity than more recently developed yeast. This is still widely used in Japan as the standard for Ginjo yeast.
No.10 yeast (Meiri yeast, Ogawa yeast, Meiriogawa yeast)
This yeast is isolated from some brewery in Northern Japan and screened at Meiri Shurui in Ibaraki prefecture. The Sake which ueses this yeast is lighter, less acidity, clean and pure with Ginjo aroma.
No.11 yeast is a variant bred from No. 7 yeast. Basically, the characteristics is the same as No. 7 yeast. This yeast has slightly more acid (especially malic acid) than No. 7 yeast, and is good at cool fermentation in high-alcohol conditions. This yeast is ideal for dry, clean and non-aromatic Sake.
No.14 yeast (Kanazawa yeast)
This yeast is developed and isolated by the Regional Taxation Bureau of Kanazawa. (Kanazawa city is a major city of Hokuriku region in Japan.) This is referred to as modern yeast compared with classic yeast like No.6, 7 and 9. This yeast created low acidity and soft Ginjo aroma like a fresh banana, and good at cool fermentation.
No. 1801 yeast
This yeast is created by crossing No.9 yeast and No.1601 yeast. This yeast ferment strongly and has low acidity and low foaming. No.1801 yeast creats a lot of aroma like an apple. The Sake which uses this yeast has performed well in competitions. However, it is said that the Sake made using this yeast can also be bitter on the palate.
Low foaming yeast
When the yeast ferment, cardon dioxide bubbles are created. This bubbles are sticky and sometimes enormous amounts as much as half the fermentation tank. In this case, extra space is needed in the tank to avoid the overflowing, and cleaning the sticky foam is needed to avoid the risk of contamination. Low foarming yeast is isolated from the mutated yeast when they yeast multipy, although the mutation rate is extremely low, and multiply them by Brewing Society of Japan. Low foaming yeast is distinguished from the original foaming version by adding the figure "01" afterwards. For exmaple, No.9 yeast is original yeast, and if the yeast name is No.901, this is low foaming yeast of No. 9 yeast.
Ambient yeast (wild yeast)
Ambient yeast is used in old days before that the science is not imporved yet. Compared with wine, ambient yeast fermentation with Sake is much risky due to the low acidity. However, these days, some Sake brewers challenge brewing Sake with using ambient yeast.
Proprietary yeast & prefectual and regional yeast
Some brewers isolated thier unique yeasts from other sources in nature, for example, flower yeast which is derived from flowers. Sometimes the yeast has prefectual and regional style which is isolated from a specific yeast strain.
Some brewers uses a combination of the yeast. It is becoming increasingly common to blend yeast.
・Add a mix of yeast strains into fermentation starter.
・Create multiple fermentation starters, and combine them when the main fermentaiton starts.
・Create different batches which uses different yeast and combine after the fermentation is completed.
Based on the research of NRIB (National Research Institue of Brewing), No.7, No.9, No.10, No.14 are relatives, although they have different characteristics. They are group No.7. However, No.6 and No.11 is similiar to them, but, they decided them different relative yeasts from No.7 group.
If you study the yeast of Japanese Sake, I think you can imagin the taste of the Sake and enjoy choicing Sake in Sake shop.