Predicting the taste of sake becomes much easier if you know the yeast being used. However, the reality is that many labels don’t display yeast information. This is the main reason why yeast is not included in the beginner’s chart below, despite being a crucial element in determining taste.
There are primarily two types of yeast: “Kuratsuki Kobo(蔵付き酵母)” (brewery-specific yeast) and “Kyokai Kobo(きょうかい酵母)” (association yeast). Kuratsuki Kobo refers to natural yeast that exists in each brewery, mainly used in Yamahai(山廃) and Kimoto(生酛) brewing methods.
On the other hand, Kyokai Kobo refers to yeast distributed by the Brewing Society of Japan. Some well-known examples include No.6 (Aramasa: 新政), No.7 (Masumi: 真澄), No.9 (Koro: 香露), No.14 (Kanazawa: 金沢), No.15 (Akita: 秋田), and No.1801. Generally, lower numbers indicate older yeasts and more traditional sake flavors, as they have been in use for a longer time, while higher numbers may indicate more modern, fruity profiles.
Previously, it was common for brewers to share yeast cultures among each other (in fact, there was also the Japanese government’s intention to increase tax revenue from sake). Therefore, some younger-numbered yeasts may bear the name of the brewer who provided the yeast. For instance, No.6, No.7 and No.9 are referred to by the brewer’s name.
Additionally, among Kyokai Kobo, you may encounter yeasts with numbers ending in “01,” indicating foamless yeast. For example, No.901 is a foamless variant of No.9 (Koro: 香霜). Foamless yeasts eliminate the need for large tanks to accommodate foam during fermentation, making post-fermentation cleaning easier for brewers.