When reading sake labels and tasting notes, you may sometimes see numbers such as 協会701号（きょうかい701ごう / Kyōkai 701）, 901号（きょうかい901ごう / Kyōkai 901）, or 1801号（きょうかい1801ごう / Kyōkai 1801）.
At first glance, these numbers can feel a bit impersonal. In reality, however, they are key factors that can greatly influence a sake’s aroma and flavor.
酵母（こうぼ / kōbo） – yeast – does more than produce alcohol. It also creates the fragrant components known as 吟醸香（ぎんじょうか / ginjō-ka） – ginjō aroma. Even with the same rice and the same polishing ratio called 精米歩合（せいまいぶあい / seimai buai） – rice polishing ratio – the character of the sake can change dramatically if the yeast changes.
In this article, we will organize three representative Kyōkai yeasts—701, 901, and 1801—from the viewpoints of aroma, acidity, and overall style. The goal is to understand them not as numbers, but as distinct “personalities.”
What Is Kyōkai Yeast?
協会酵母（きょうかいこうぼ / Kyōkai kōbo） refers to sake yeast strains isolated and cultivated by the Brewing Society of Japan, and distributed to breweries across the country. The “No.” is basically assigned in the order in which the strains were isolated.
Many Kyōkai strains originally come from excellent 蔵付き酵母（くらつきこうぼ / kuratsuki kōbo） – brewery-resident yeasts – that produced outstanding sake. That is why each strain has a clear personality.
Among them, 701, 901, and 1801 are representative yeasts that are widely used today.
Kyōkai No. 701 — A Balanced Benchmark
No. 701 belongs to what is commonly called the “No. 7 line.” No. 7 yeast is historically important—it supported postwar sake brewing—and it is well known for stability and good balance.
In terms of aroma, it tends to create a gentle ginjō aroma centered on 酢酸イソアミル（さくさんいそあみる / sakusan isoamiru） – isoamyl acetate (banana-like aroma). カプロン酸エチル（かぷろんさんえちる / kapuronsan echiru） – ethyl caproate (apple-like aroma) – is not especially strong.
It also tends to produce slightly firmer acidity, making it easier to achieve a well-harmonized overall profile.
It pairs well with designs that do not overemphasize aroma—such as junmai styles and food-friendly sake—and can be seen as a “basic form.”
It may not be flashy, but its strengths are stability and high reproducibility.
Kyōkai No. 901 — A Symbol of the Ginjō Style
No. 901 is an improved type of No. 9 yeast. No. 9 is widely known as a yeast that contributed greatly to the development of ginjō sake.
Its biggest feature is that it produces a larger amount of ethyl caproate. It creates a bright, apple-like ginjō aroma and often results in a clean, transparent style.
Its acidity tends to be slightly lower than No. 701, giving a lighter impression.
It is well suited to ginjō sake and aroma-focused designs, and it can be said to have shaped the modern image of Japanese sake.
No. 901 is a classic representative of “aromatic sake.”
Kyōkai No. 1801 — An Evolved High-Ester Type
No. 1801 is a high-ester-producing yeast that further develops the No. 9 line.
It generates a very large amount of ethyl caproate, so the bright ginjō aroma appears more strongly. In addition, it tends to produce lower acidity, resulting in an overall impression that is clean and refined.
It suits daiginjō and competition-oriented designs, and it is a good match for styles that clearly showcase aroma.
If No. 901 is the benchmark of the ginjō type, then No. 1801 is easier to understand as its “enhanced version.”
Why Does the Aroma Change?
During fermentation, yeast not only converts sugars into alcohol, but also produces esters through fatty-acid metabolism.
Ginjō-aroma components such as ethyl caproate and isoamyl acetate vary in production depending on differences in yeast enzyme activity and metabolic pathways.
In addition, fermentation temperature and nutritional conditions also affect the production of aromatic compounds.
In short, a yeast’s “personality” is determined by its metabolic characteristics—namely, which aromatic compounds it produces, and how much.
Comparing the Three
| Yeast | Aroma | Acidity | Style Tendency |
|---|---|---|---|
| 701 | Gentle (banana-leaning) | Somewhat firm | Balanced type |
| 901 | Bright (apple-leaning) | Slightly lower | Ginjō type |
| 1801 | Very bright (strong apple) | Lower | Best for daiginjō |
When organized this way, 701 → 901 → 1801 can be understood as a flow of “aroma enhancement.”
Think of Them as “Aroma Evolution,” Not Just Numbers
701 is the benchmark type.
901 is the ginjō type.
1801 is the high-ester type.
Rather than memorizing the numbers as isolated facts, it becomes easier to organize them as “stages in aroma evolution.”
Yeast is a crucial design element that determines a sake’s character.
Just by paying a bit of attention to the yeast number written on the label, the world of sake starts to look much more three-dimensional.
Behind each number lies a set of metabolic traits that shape the sake’s final profile.
Next: Understand “Labeling and Classification”
So far, we have looked at the structure of sake through the lens of “ingredients and design,” including 酒母（しゅぼ / shubo） – fermentation starter – sake rice, and yeast.
So how is that design expressed on the label?
純米酒（じゅんまいしゅ / junmai-shu） – junmai sake – 吟醸酒（ぎんじょうしゅ / ginjō-shu） – ginjō sake – 大吟醸酒（だいぎんじょうしゅ / daiginjō-shu） – daiginjō sake.
What are 特定名称酒（とくていめいしょうしゅ / tokutei meishō-shu） – special designation sakes?
What do the polishing ratio and added alcohol mean?
Now that you understand the ingredients, the meaning of labeling begins to look more three-dimensional.
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