Sake yeast (清酒酵母)

Sake yeast is the generic term referring to yeasts used for brewing sake (Japanese liquor). It is one of the factors that greatly affect the flavor and aroma of sake. Most of the yeasts are classified under budding yeast (Saccharomyces cerevisiae), among which strains with a particularly high brewing quality are selected for use. Instead of using just one kind of strain, sake is usually made from a blend of sake yeast mashes, or by blending finished sake liquors, thus combining the merits of each strain.

For your information, some experts dispute about yeasts that have already been classified under Saccharomyces cerevisiae.

Sake yeasts comprise foam-forming kyokai sake yeasts, which are high producers of foam, and non-forming kyokai sake yeasts, which are low producers of foam, the latter of which having a higher productivity. Sake yeasts are distributed by laboratories or research institutes of Brewing Society of Japan or local municipalities, in addition, some universities and breweries isolate and culture them on their own. Sake yeasts are distributed in the forms of Kyokai sake yeasts, Kyokai sake yeasts, Kyokai sake yeasts, or dried yeasts. When using dried yeasts, shubo (yeast mash) is unnecessary.

History
Premodern times
Presumably, sake was first made by taking in naturally residing yeasts accidentally. Later, it was made by applying traditional techniques, or using 'Kuratsuki kobo' or 'Ietsuki kobo' (yeasts living in the brewery), however it was hard to stabilize the sake quality, and, even when good sake was produced, 'reproducing exactly the same one' wasn't attainable. The scientific reproducibility was a major problem.

Even in ancient times, when the modern term 'fermentation' didn't exist, it was well known that adding 'something' to rice and water will turn the mixture into sake, and this 'something' was called koji (malted rice), moto (yeast mash), or shubo. In China, which belongs to the same liquor culture region of multiple parallel fermentation, fermentation was already called 'Ko' in the age of the Sung dynasty, according to a brewing treatise titled "Hokuzan Shukei" (book on brewing technique), the preface of which is known to be written in 1117.

Modern times
In the West that belongs to the liquor culture region of single-fermentation where ingredients turn into liquor without adding 'something,' the existence of yeasts was scientifically proven only in the 19th century. Because Saccharomyces cerevisiae, that comprises not only sake yeasts but also beer yeasts, wine yeasts and bread yeasts, was discovered by J. Meyen in the 1830's, and named as such by E.C. Hansen around 1882, it is also referred to as Saccharomyces cerevisiae Meyen ex Hansen.

Modern brewing techniques were introduced to Japan in the Meiji period, on which occasion an English word yeast and a German word Hefe were imported to refer to 'microorganisms that promote fermentation' in the course of studying beer brewing techniques instead of sake brewing techniques. In 1874, '醗酷' accompanied by its readings 'hakko' and 'yasuto,' which means yeast, appeared in "Kagaku Shokei Shusui Seizo-sho Zen" (scientific expedient of sake brewing) written by H. Caliberd and translated by Harue Koizumi. Yasuto' is what we call yeast today.

In a book published in 1888, the scientific name Saccharomyces cerevisiae was phonetically written as 'サッカロミセス・セレウヰシェ-,' and explained as 'microorganisms used for brewing liquor or making bread.'
According to the reference offered by Brewing Society of Japan, translations such as '酵母(yeast)' or '清酒発酵母 (sake yeast)' first appeared in brewery magazines in the period during 1889 to 1890, which were described variously as '酵母,' '清酒酵母,' '醸母,' '醸母菌,' or 'イ-スト' for some time.

In fact, it was during that period that Japan was struggling to form foundations for modern zymurgy. In 1893, Dr. Kikuji YABE, who was a Japanese zymologist, isolated sake yeast from Nihonshu moromi (raw unrefined sake) of sake. In 1895, it was named after the zymologist and presented at an international symposium as Saccharomyces sake Yabe. In 1904, the National Research Institute of Brewing was established under the Ministry of Finance. This is the forerunner of the present-day National Research Institute of Brewing (NRIB).

Over the course described above, various translations for yeast or Hafe were unified as '酵母.'

Although the person who coined the translation is unknown as of year, it was presumably named as such because of the fact that '酵' had long been a letter meaning fermentation in Asia, and '母,' which had also been written as '酒母' and read as 'moto (origin),' had been a letter meaning an origin of all creation or phenomena.

Later, Yamahai-jikomi (a method of yeast-mash making) was developed in 1909, Sokujo-kei (seed mash made by the quick fermentation method) for sake was developed in the next year (1910), and the first Zenkoku Shinshu Kanpyokai (National New Sake Appraising and Deliberating Fair) was held in 1911. Over time, a system for Brewing Society (present-day Brewing Society of Japan) to isolate, pure-culture, and distribute the high-prize winning yeasts that were objectively evaluated as excellent at the fair to breweries throughout Japan was established. Such yeasts are called Kyokai sake yeasts today.

Present day
In the 1920's, from the Taisho period through the early Showa period, the National Institute of Brewing conducted researches for higher quality sake, and during the course production of sake yeasts for making archetypes of sake which were later developed and spread as Nihonshu ginjo-shu (high-quality sake brewed at low temperatures from rice grains milled to 60 % weight or less) began.

In order to produce ginjo-shu, improvements in various fields such as rice polishing and other technologies in addition to yeasts are required, and then in the 1970's, a breakthrough in temperature control technology in the Nihonshu moromi-zukuri (preparation of final mash) process and realization of new yeasts such as Sake yeast kyokai No.7 and Sake yeast kyokai No.9 enabled brewers to produce Nihonshu ginjo-shu and junmai (sake brewed with only rice, water, and koji without additives) ginjo-shu.

In response to the ginjo-shu boom in the 1980's and later, many yeasts that yield a high aroma, such as low-acid-producing yeasts, high-ester-producing yeasts, and high-malic-acid-producing yeasts, were developed, and research institutes under prefectural governments and agricultural colleges promoted development of new types of yeasts. These are explained in 'Yeasts developed by local municipalities,' 'Yeasts developed by colleges,' and 'Yeasts developed by companies and private institutes' in this section.

Characteristics
Kyokai kobo (Kyokai yeast)
Yeasts distributed by the Brewing Society of Japan
Refer to Kyokai-kei kobo (Kyokai sake yeast) for detail.

Yeasts developed by local municipalities
Yeasts developed by laboratories and research institutes under local municipalities, such as industrial technology centers and brewing laboratories. In most cases, sake yeasts are designed to make the best of them from their development phase, taking into account the sake brewing using 'sakamai (rice for brewing sake) developed by each local municipality in sakamai producing areas,' taking advantage of local natural conditions including climate and soil.

Amid the trend for local consumption of locally produced products, development of superior yeasts along with sakamai is the key factor for local municipalities to improve the local sake quality and reconstruct the local industries. These backgrounds have intensified competition for yeast development to the extent that there are fewer prefectures that do not have any municipally developed yeasts today. However, those locally developed yeasts are not necessarily confined within the prefecture, but some of them are used in other prefectures or adopted as a Kyokai yeast. Also, they are often used as a parent strain to be bred with other yeasts to develop new yeasts used in and out of the region.

Aomori yeast
Aomori yeasts are developed jointly by Aomori Industrial Research Center, Technical Research Institute of Hirosaki area and Brewing Society of Japan.

Mahoroba Hana yeast
Developed in 1998. A non-foaming mutant strain isolated from moromi in a brewery in the prefecture and cultured. It is used for junmai-shu (sake made without added alcohol or sugar) made from Hanafubuki, which is a rice brand grown in the prefecture.

I-go yeast/ro-go yeast
Developed in 2002. A high caproic-acid-ethyl-producing yeast which is a cerulenin-resistant mutant strain derived from Mahoroba Hana yeast. Used for daiginjo-shu (super high-quality sake brewed from rice grains polished to 50 percent weight or less) made from Hanaomoi, which is a rice brand grown in the prefecture. Another yeast under development is a high isoamyl-acetate-producing yeast, which is a trifluoroleucine (leucine analog)-resistant strain derived from Mahoroba Hana yeast.

Iwate yeast
Iwate yeasts are developed jointly by Iwate Industrial Research Institute in Iwate Prefecture and Iwate Biotechnology Institute/Iwate Biotechnology Research Center. The institutes also develop wine yeasts.

Ginjo 2-go (Ginjo No.2)
Developed in 1993. An yeast isolated from moromi in a brewery in the prefecture and cultured. Produces twice as much ethyl caproate than Sake yeast kyokai No. 9 yeast.

YK-45
Developed in 1998
A strain cross-bred by genetically engineering yeasts owned by the center. It has a mellow aroma, and well-balanced flavor. It is a high isoamyl-acetate-producing yeast.

YK-71
Developed in 1998. A strain cross-bred by genetically engineering yeasts owned by the center. It is a high caproic-acid-ethyl-producing yeast that yields a high ginjo aroma.

Miyagi yeast
Miyagi yeasts are developed jointly by Industrial Technology Institute of Miyagi Prefecture and Miyagi Sake Brewers Association.

Miyagi yeast (Shodai [first generation])
An yeast isolated from ginjo moromi (the main mash for ginjo-shu) used in Saura brewery, which is the producer of "Uragasumi," by Kazuo SATO and others of the brewing laboratory of Sake Makers' Association of Miyagi Prefecture in 1965. It was distributed as Sake yeast kyokai No. 12 from 1965 to 1995. The yeast yields a type of moromi fermented for a long period at a low temperature, which is suited for making ginjo-shu having a high aroma.
It is also called 'Uragasumi yeast.'

Miyagi-my yeast (MY-3102)
Developed in 2000. It was obtained by selecting strains having high alcohol resistance and producing low acid from shodai Miyagi yeast. It is used for junmai-shu and junmai ginjo-shu.

Manami yeast (MY-2142)
Developed in 2002. A mutant strain derived from Sake yeast kyokai No. 7 having low diacetyl accumulation. It is used for low-alcohol sake.

Non-foaming Miyagi-my yeast (MY-3227)
Developed in 2004. It is a non-foaming mutant strain of Miyagi-my yeast.

Akita yeast
Akita yeasts are developed jointly by the brewing laboratory of Akita Research Institute for Food and Brewing and Akita Sake Brewers Association. Akita Research Institute for Food and Brewing also develops wine yeasts, beer yeasts and bread yeasts.

Akita-Ryu-Hanakobo (AK-1)
Developed in 1990. A non-foaming yeast selected from more than 900 strains collected from moromi and moto used in the breweries in the prefecture. Based on the result of DNA testing, it is deemed as a mutant strain of Sake yeast kyokai No. 7. At Zenkoku Shinshu Kanpyokai (National New Sake Appraising and Deliberating Fair) held in the brewing year 1990, on which occasion Akita Prefecture sent sake using the yeast, the prefecture won the second largest number of gold prizes in the nation. It has been distributed as Sake yeast kyokai No. 1501 since 1996. It produces high ethyl caproate, shows good fermentation at a low temperature, has a high sake aroma, and produces low acid. It is used for daiginjo-shu and junmai daiginjo-shu.

AK-2F
Developed in 1994. It produces tasty sake, with a mild aroma, minimal acid, and light finish. It is a foaming yeast. It is mainly used for junmai-shu and honjozo (authentically-brewed)-shu.

AK-3F
Developed in 1994. It produces tanrei (crispy and dry) sake, with a mild aroma, minimal acid, and light finish. It is a foaming yeast. It is mainly used for junmai-shu and honjozo-shu.

AK-3
Developed in 1997. It is a non-foaming mutant strain derived from AK-3F, and has characteristics similar to AK-3F, producing little amino acid. It is mainly used for junmai-shu and honjozo-shu.

Akita-Ryu-Miyabikobo (AK-4)
Developed in 1998. It is a non-foaming yeast for low-alcohol sake. It has a glamorous and fruity sake aroma.

Komachi yeast
Developed in 2003. The yeast is a selection of strains isolated and cross-bred from 6 yeast strains of ginjo-shu used nationwide. It features a sake aroma more glamorous than Akita-Ryu-Hanakobo, and a full flavor that comes with the sake aroma. It is used for ginjo-shu made from Akita sake Komachi, which is a prefecture-grown rice suited for sake brewing.

Akita Junmai yeast
Developed in 2004. The yeast was selected from strains cross-bred/bred using a ginjo yeast as the parent strain. It has a well-balanced aroma, produces moderate acid, and its aroma and flavor are well-balanced. It is mainly used for junmai-shu.

Yamagata yeast

Fukushima yeast
It is developed by Fukushima Technology Centre, Aizu-Wakamatsu Technical Assistance Centre.

Utsukushima-yume yeast (F7-01)
Developed in 1991. It is a mutant strain derived from Sake yeast kyokai No. 7. It produces little acid and has a gentle flavor and high aroma. Among others, it produces 4 times as much ethyl caproate as kyokai No. 7.

Yeasts developed by colleges
Hanakobo (flower yeast) and others.

Yeasts developed by companies and private institutes
In recent years, dry yeasts imported from Mauri Yeast Australia are commercially available.

The two products available are "Sakura" and "Fuji."

Most of the breweries have proprietary (developed) yeasts commonly called Kuratsuki-kobo to be used for brewing. Drying of such proprietary yeasts is outsourced to private institutes (such as Shinwa Foods Chemical).

Overview of yeast phylogeny

Terminology
Strain, microbiological context
Resistant strain
Mutant strain
Auxotroph
Cross breeding strain
Hyper-producing strain