Yeast is the unsung hero of sake brewing. It goes without saying that without it you cannot produce alcohol. Therefore, a strain that is both reliable and ferments vigorously is an integral component of sake's few ingredients. The type of yeast used also plays a crucial role in much of the characteristics in sake, with a particular influence on aroma and acidity. As these two factors heavily influence our perception of taste, it could be argued that yeast is more crucial in determining the final flavour components than even the variety of rice.
The yeasts used in sake brewing, known in Japanese as seishu kobo, belong to the Saccharomyces Cerevisiae species, and are cousins of those used to make beer and wine. What sets them apart from other strains is their ability to remain active at the low temperatures often used when brewing sake. They also have a greater capacity to produce high levels of alcohol, with most naturally fermenting to around 16-18% abv. Some extreme strains have even been known to break the 21% limit of what is permissible before it can no longer be classified as sake. This is one of the reasons why sake is the highest naturally fermenting beverage in the world.
In the past, brewers relied on wild yeasts (yasei-kobo), often referred to as ambient (yane-tsuki, ie-tsuki), such as those naturally present in the air or clinging to machinery. This suited the two traditional brewing techniques of kimoto and yamahai (methods of making yeast starter) that were the norm up until the beginning of the 20th century. However, with the development of the modern sokujo method, there quickly became a need to have readily available and reliable yeasts that are necessary when using this technique. Therefore, in 1907 the newly formed Brewers Society of Japan began distributing cultivated strains collectively known as Association Yeasts (kyokai kobo).
Initially, only one strain, designated as simply "First Class Yeast", was distributed. However, this later expanded to the numbered system that is still in place today. Suitable strains were first identified at breweries with a tendency to produce exceptionally high quality sake before later being made commercially available. At the time, these breweries were mostly located in the two powerhouse regions of Nada in Hyogo Prefecture and Fushimi in Kyoto. As techniques progressed, this shifted to those in and around the region of Saijo in Hiroshima Prefecture, which now completes a trio known as The Big Three Sake Regions (sandaisaketokoro). Therefore, it is not surprising that the first five Association Yeast's were all isolated at breweries in one of these three regions.
However, the mainly conservative industry at the time were said to be slow to adopt these radical new cultivated yeasts. It wasn't until #6, isolated at Aramasa Shuzo in Akita Prefecture, that their usage started to become more widespread. Unlike the first five, #6 was lower in acidity, more consistent and could survive colder temperatures. When word spread of its ability to produce superior sake the uptake of Association Yeast finally started to take off. By 1940, during the Second World War, this was the only yeast available for distribution. As it is currently still available to brewers, it has become the oldest strain still in circulation.
Nowadays, there are numerous different styles of cultivated yeasts available to brewers. Association Yeasts are also not the only source, with a few prefectures developing their own series of suitable yeasts that compliment their region's typical style. Their development has also been heavily influenced by changing consumer trends, with a tendency for the newer strains to produce incredibly high aromatics. In particular, the ginjo boom that began in the 1980's led to modern mutated strains being developed that were high in the two ester compounds Ethyl Caproate and Isoamyl Acetate. The latter, known for producing banana-like aromas, and the former more appley ones, are now considered crucial components in conventional ginjo sake.
The development of increasingly more diverse strains of sake yeast has continued in earnest over the decades since the first Association Yeast was introduced back in 1907. As makers now look for new ways to differentiate their sake within an increasingly crowded premium market, several prefectures or brewing institutes have stepped up their efforts in order to try and create the next exciting yeast strain. As a result, the variety currently available to brewers is bigger than it has ever been before.
Given the influence these yeasts have on sake, this can only be good news for consumers. Furthermore, although perhaps not as interesting for most as learning about rice varieties, it is also worthwhile getting to know a bit about the yeasts that are currently in circulation, and the evolutionary journey they have taken over the decades. Therefore, the following is a brief summary of the early Association Yeasts, followed by those currently in circulation, as well as some of the more popular regional varieties that have appeared in recent years.
Sake made from Association Yeast # 1
Discontinued Association Yeasts
Association Yeast #1 / 協会号
Isolated in 1906 from a yeast starter (shubo, moto) at Sakura-Masamune in Nada, Hyogo Prefecture. It was distributed nationally as an Association Yeast between 1916 - 1935.
Very muted aromas, and often said to produce high acidity. However, some of the few remaining brewers who still use this strain have reported otherwise.
Association Yeast #2 / 協会二号酵母
Isolated in the late Meiji Period (1868 - 1912) from new sake (shinshu) at Gekkeikan in Fushimi, Kyoto. It was distributed between 1917 - 1939.
It is said to produce rich sake with a good taste. However, it is also rumoured to be high in acidity compared to more modern strains.
Association Yeast #3 / 協会三号酵母
Isolated in 1914 from new sake (shinshu) at Suishin in Mihara, Hiroshima Prefecture.
Highly rated at the time, it was later discontinued in 1931 after degeneration during storage.
Association Yeast #4 / 協会四号酵母
Isolated in 1924 in Hiroshima Prefecture, the location of the brewery is unfortunately unknown. Highly rated, and known to produce some good aromatics, it was also discontinued in 1931 due to degeneration during storage.
Association Yeast #5 / 協会五号酵母
Isolated in 1923 from both new sake (shinshu) and a yeast starter (shubo, moto) at Kamotsuru in Saijo, Hiroshima. It was distributed between 1925-1936.
It is said to have been highly rated at the time, and produces fruity aromas. These aromas are now considered to be components of orthodox ginjo sake (ginjo-ka).
Association Yeast #12 / 協会十二五号酵母 (Also known as Urakasumi Yeast / 浦霞酵母 and the First Generation Miyagi Yeast 初代宮城酵母)
Isolated in 1965 at Urakasumi Shuzojo in Miyagi Prefecture, where it is currently still the house yeast, this was distributed as an Association Yeast from 1986 to 1995.
It is said to be particularly suited to brewing ginjo sake, producing very high aromatics with a strong tolerance of low temperatures.
Vials of various Association Yeasts
Current Association Yeasts
Association Yeast #6 / 協会六号酵母 (Also known as Aramasa Yeast / 新政酵母)
Isolated in 1930 at Aramasa Shuzo in Akita Prefecture, this yeast was the only Association Yeast available during the Second World War.
Noted for its gentle aromas, #6 is a vigorous-fermenting yeast that can survive very high alcohol. As a result, it is capable of producing very dry sake. It can also withstand very low temperatures, as per the winter climate in Akita Prefecture.
The first widely used strain from amongst the Association Yeasts, this is one of the most significant in the history of sake yeasts. Furthermore, the low temperature, long-term fermentation style of Akita, using this yeast, is said to have become the blueprint for future ginjo brewing.
Association Yeast #7 / 協会七号酵母 (Also known as Masumi Yeast/ 真澄酵母)
Isolated in 1946 at Miyasaki Shuzo in Nagano Prefecture by Dr Shoichi Yamada of the Nation Research Institute of Brewing (NRIB).
Like #6, it is vigorous-fermenting and very stable. However, #7 also produces ginjo aromas, and was at one time the yeast of choice for entries to the Annual New Sake Competition (zenkoku-shinshu-kanpyokai).
Although it is often used nowadays for lower grade sake, it is still capable of producing good quality ginjo as well. Due to this versatility, it is currently the most widely used sake yeast in existence. Moreover, there are many other yeasts that have been derived from #7, which are now collectively referred to as #7 Lineage Yeasts.
Association Yeast #9 / 協会九号酵母 (Closely derived from Kumamoto Yeast / 熊本酵母)
Isolated in 1953 as Kumamoto Yeast at the Kumamoto Prefectural Brewing Research Centre in Kyushu. It was first made available as an Association Yeast in 1968.
As it produces less acidity, can vigorously ferment at lower temperatures, and typically produces much more pronounced aromatics than #6 and #7, it has been a popular yeast in ginjo production ever since its initial release. It dominated the entries to the Annual New Sake Competition up until the 1990's when it was finally surpassed by more modern, highly aromatic strains. It is also the K (Kumamoto) in the YK35 formula, once thought to be the winning recipe in the aforementioned competition. (Y stands for Yamada-Nishiki, and 35 is said to be the ideal polishing percentage)
One last interesting thing of note: although not in any way important to its brewing ability, #9 produces a very light coloured foam in the mash which is particularly pleasing on the eye.
*** Although the original Kumamoto Yeast is often referred to as #9, a previous toji of mine noted that it produces higher levels of acidity than the Association version. There also exists several derivatives of #9 listed as KA Yeasts ***
Association Yeast #10 / 協会十号酵母 (Also known as Ogawa - Meiri Yeast /明利小川酵母)
Originally selected from samples taken from fermenting mash (moromi) in each of the six prefectures in Tohoku, the northernmost part of Japan's main island Honshu. This was carried out by Dr Chikawa Ogawa, the president of the Meiri Shurui brewery in Ibaraki Prefecture. In 1958, it was made available regionally through the Ibaraki Prefectural Food Research Institute and Meiri Shurui. It was finally made available nationally as Association Yeast #10 in 1977.
Ferments best at low temperatures, resulting in lower acidity than #9. It has much more pronounced ginjo aromas than its predecessor. Because of these characteristics, it is most widely used in the Tohoku region to make the signature light and crisp (tanrei karakuchi) style of sake .
Association Yeast #11 / 協会十一号酵母
The first of the Association mutant strains, this was derived from #7 in 1975. It was later made available by the Brewing Society of Japan in 1978.
Although it has much the same characteristics as the original #7 it is extremely resistant to alcohol. As a result, it is sometimes referred to as Alcohol Resistant Yeast (アルコール耐性酵母 ). Due to this tolerance, it is ideal for long term fermentation, and is often used to brew very dry sake.
Other characteristics worth noting are its tendency to produce sake low in amino acids, with a slightly higher than usual acidity.
Association Yeast #14/ 協会十四号酵母 (Also known as Kanazawa Yeast 金沢酵母)
First isolated in 1922, #14 essentially superseded #12 in the Association line-up. It was introduced in 1995 after being selected from amongst numerous other strains stored at the Kanazawa Regional Tax Agency. As this agency overseas Ishikawa, Fukui and Toyama Prefecture it has become synonymous with the Hokuriku Region.
As it produces very low acidity and pronounced ginjo-ka it is said to be more suited for ginjo brewing, particularly those with highly polished rice. It is also ferments well at the low winter temperatures that the Hokuriku region is famous for.
Association Yeast #15/ 協会十五号酵母 (Also known as AK-1)
Isolated in Akita Prefecture where it was referred to as AK-1, it became Association Yeast #15 in 1996.
Although it produces very fragrant sake, the yeast is said to be rather temperamental. It is best suited to low temperature, slow fermentation.
The following are both a continuation of the Association Yeasts currently in circulation and the latest non-foaming yeasts that are now widely used across Japan. All non-foaming yeasts can be identified by the 01 digits after their regular nomenclature. Currently, #6,7,9,10,14 and 15 all have foamless counterparts. However, the remaining Association Yeasts below are only available as non-foaming.
Because these yeasts don't form a tall head of foam during fermentation, the volume of sake can be increased in each tank, thus improving a breweries space efficiency. They also alleviate the dangerous and time consuming work of cleaning the foam that sticks to the side of the tank as it rises and falls during fermentation. However, the downside is that the various stages of transformation that the foam undergoes acts as a very dependable visual guide to the brewers. These can be extremely important when analysing the various stages of fermentation, and can offer early warning signs that something is not right in the main mash.
It is also important to note that, although the characteristics of these yeasts are said to be identical to their foaming counterparts, there are several brewers that have experience using both who have said this is not the case. They report that they are not quite as vigorously fermenting.
Association Yeast #1601/ 協会1601号酵母 (Also known as Hachiroku 86)
Originally developed by Gekkeikan as Hachiroku Yeast, #16 is a crossbreed of Association #7 and #1001.
One of the yeasts that comes under the description of "High Aroma Component Productive Yeast" due to its extremely prominent ginjo-ka, particularly the aforementioned ethyl caproate.
The aromas created by yeasts such as #16 are so dominant that the sake made from them are often classified by brewers separately from other sake as kaporon-san kei, or belonging to the caproate classification.
Association Yeast #1801/ 協会1801号酵母
A cross between Association #1601 and #9, this also produces very high levels of ethyl caproate.
With better balance than #1601, this yeast has become a very popular choice for brewing Daiginjo for entry to the Annual Japan Sake Awards. However, as is common with high aroma producing yeasts, it is relatively weak during fermentation, which typically leads to slightly sweeter sake.
Sake made from Kochi's highly aromatic CEL-24 Yeast
Kochi Yeasts / 高知酵母
The work of the Kochi Prefectural Industrial Technology Centre, these yeasts were created in order to support the 18 active sake breweries in Kochi Prefecture. Their development has helped establish a strong regionality within Kochi Sake, and is indicative of the unity that exists within the prefecture's sake industry.
Developed in 1992, this yeast produces a strong fermentation and is tolerant to high alcohol. Often leads to light sake low in amino acids, it also produces a high concentration of isoamyl acetate. On paper, this is the perfect representation of Kochi's dry, crisp and aromatic style of sake.
Developed in 1993, this yeast, and its CEL-24 sibling have become synonymous with the highly fragrant ester ethyl caproate and the Kapuron-kei sake it produces. Isoamyl acetate is on the low side, with a higher than usual production of malic acid. This often leads to a nice refreshing acidity.
Developed in the same year as CEL-19, this yeast produces incredibly high levels of ethyl caproate and malic acid, said to be around twice as high as its counterpart. However, the downside to this is its fermentation ability is weak, and relatively unstable. As a result, it is said to be best for producing sweat sake with a sour fragrance, typically of lower alcohol content.
Developed in 1995, it is a strong fermenting yeast that produces far less ethyl caproate than CEL-19, yet is high in isoamyl acetate. Acidity is also well balanced.
Developed in 1991, this is a combination of wine yeast and sake yeast. It produces sake that displays the characteristic flavours and aromas of wine, yet with the superior fermentation power of sake.
Like Kochi, Hiroshima Prefecture has a particularly tight Brewers Association. The NRIB (Nation Research Institute of Brewing) is also based in the brewing hub of Saijo, in eastern Hiroshima, having moved from its initial base in Tokyo back in 1995.
A lot of research has gone into developing a group of strong yeasts that are suitable for brewing Hiroshima's clean and refreshing style of sake made from soft water.
Flower Yeast / 花酵母
In an attempt to diversify the flavours and aromas in sake, research began at the Tokyo University of Agriculture in the early 2000's to identify suitable yeasts from flowers. They later formed a dedicated department, the Society of Hanakoubo Research in order to further develop a core of about 14 strains deemed suitable for making quality sake.
Although not widely used, there are a few breweries that have heavily adopted their use, producing some very interesting and unique sake.
Currently there are around 25 breweries utilising Flower Yeasts in some capacity, with one or two of them using them for their entire production. Popular examples include those isolated from strawberry plants, sunflowers and various types of rose.
M310 (Also known as Meiri Yeast / 明利酵母)
A derivative of Association #1001, and developed by the same brewery. It was first developed in 1992 and later made available nationally in 1995. However, it was never included as an Association Yeast and was available instead through the aforementioned Ibaraki Prefectural Food Research Institute.
Like #10 this yeast is low in acidity, and ferments strongly at low temperatures. However, it produces much higher levels of ethyl caproate than its older relative. It also proved to be very popular for making Daiginjo grade sake for use in the Annual Japan Sake Awards.
The name M310 is a clever use of wordplay: Three in Japanese is "mi" and ten in "to", which is a reference to the Meiri Brewery's home town of Mito, in Ibaraki Prefecture.