RICE. WATER. KOJI. MAGIC!

In the captivating world of sake, where rice grains transform into a divine elixir, there's an unsung hero that deserves its spotlight: yeast. Often overlooked in favour of rice and water, yeast is the silent magic behind sake's diverse flavours and captivating aromas. Without yeast, the alchemical dance of turning sugars into alcohol and carbon dioxide, central to the creation of all alcoholic beverages, would remain unfulfilled.

The Role of Yeast in Sake Brewing

Yeast's importance in the sake-making process extends beyond mere fermentation. It holds the key to shaping the very essence of sake, impacting its fragrance, flavour, and overall character. A reliable and robust yeast strain is an essential ingredient, ensuring vigorous fermentation, high alcohol content, and the development of intricate taste profiles.

Through fermentation, yeast produces compounds like esters, alcohols, and acids, each contributing to the unique tapestry of fragrance and taste. The temperature at which fermentation occurs is also critical, as this dictates which compounds flourish, influencing the degree to which the yeast will mould a sake's character.

YEAST IN EARLY PRODUCTION

In bygone eras, brewers relied on naturally occurring wild yeasts, known as "yasei-kobo" or ambient yeasts, as these microorganisms were naturally present in the air or adhering to brewery equipment. This reliance on wild yeasts evolved with the two established traditional brewing methods, kimoto and yamahai, both of which involved cultivating yeast starters. These practices held sway until the dawn of the 20th century.

However, as the modern sokujo method of sake production emerged, there arose a pressing demand for consistent and readily accessible yeast strains that aligned with this innovative technique. To meet this need, in the year 1907, the newly established Brewers Society of Japan embarked on the distribution of deliberately cultured yeast strains, collectively referred to as "Association Yeasts" or "kyokai kobo." This transformative shift marked a significant juncture in the evolution of sake brewing, as it introduced a more controlled and predictable element into the art of sake production.

Modern Sake Yeasts

Association Yeasts marked a turning point in the industry's yeast selection. Today, an array of yeast varieties is available to brewers. The ‘ginjo boom’ of the 1980s spurred the development of strains rich in ester compounds, like Ethyl Caproate and Isoamyl Acetate, which create captivating aromas, from apple-like notes to powerful scents of strawberry and banana.

Yeast development is a journey of isolation and cultivation. Strains are often isolated from the foam atop fermenting mash. This painstaking process takes years, as researchers work to uncover yeasts with desired traits. The resulting strains shape sake production, offering the potential for novel and exciting flavour profiles.

Awa-Nashi, or foamless yeasts, have revolutionised brewing by eliminating the need for extensive foam management during fermentation. While these variants brewers save time and cost, debate continues among the sake fraternity on their impact on the final product's refinement..

The Diversity of Sake Yeast

Regional pride and innovation remain driving forces in yeast development even today. Prefectures and brewing institutes have developed their own yeasts, aligning with local water and rice characteristics to discover new points of differentiation. Proprietary strains and regional variations create diverse expressions of sake, enriching the industry's landscape.

In modern sake, yeast's influence on the quality of the final product is undeniable. Emerging strains have propelled the industry forward, differentiating premium offerings from standard fare. Discerning consumers can now find yeast information on sake labels, empowering them to explore and appreciate the nuances yeast imparts.

Notable Yeast Strains

Yeast #1 to #6 (No longer in use)

These yeast strains, identified as #1 to #6, are no longer employed in sake production due to their high acidity, which rendered them unsuitable for contemporary brewing techniques. They were among the early experimental yeast strains used in sake production but have been replaced by more suitable options. While they are no longer in circulation, they represent a part of sake history, marking the evolution of yeast selection and brewing practices.

Yeast #7 (Masumi)
- Yeast #7, known as "Masumi," is celebrated for its mellow fragrance and robust fermentation capabilities. Its versatility makes it the most commonly used yeast in sake production across Japan. This yeast is cherished for its ability to produce sake with a balanced aroma and taste profile. It is known to thrive under various fermentation conditions, contributing to its widespread popularity among brewers.
Yeast #8 (No longer in use)
- Yeast #8, like its predecessors #1 to #6, is no longer in use due to its high acidity, which was considered too strong for modern sake brewing methods. Although it is not actively employed today, it represents an earlier phase in yeast development in Japan's sake industry.
Yeast #9 (Koro)
- Yeast #9, affectionately referred to as "Koro," is highly regarded for its remarkable fragrance and steady fermentation performance. This yeast is the preferred choice for crafting ginjo-shu, a premium sake variety known for its delicate and complex aroma. Koro yeast's ability to impart captivating scents to sake, combined with its resilience during fermentation, has made it an indispensable yeast strain in the sake world.
Yeast #10 (Tohoku Moromi)
- Yeast #10, often identified as "Tohoku Moromi," is prized for its contribution to sake's flavour profile. It imparts a low level of acidity and bestows a fine-grained, subtle taste to the sake it ferments. This yeast is commonly employed in the Tohoku region, known for its distinctive sake style. Brewers value yeast #10 for its ability to craft sake with a gentle and refined character, making it a choice yeast for those seeking a milder taste experience.
Yeast #11 to #13 (No longer in use)
- Yeast strains #11 to #13 have also fallen out of use due to their high acidity levels, making them unsuitable for modern sake production techniques. While no longer in circulation, these yeast strains played a role in the historical development of sake yeast selection.
Yeast #14 (Kanazawa Kobo)
- Yeast #14, also known as "Kanazawa Kobo," is prominently featured in Shizuoka's sake production. It stands out for its low acidity and the delightful fragrances reminiscent of pears and apples that it imparts to the final brew. This yeast adds a fruity and refreshing dimension to sake, aligning with Shizuoka's reputation for approachable, aromatic, and enjoyable sake varieties. Kanazawa Kobo's contributions make it a favoured yeast strain in the region.
Yeast #15 (Akita Moromi or AK-1)
- Yeast #15, often referred to as "Akita Moromi" or simply "AK-1," boasts a lively and characteristic fragrance that sets it apart. However, it requires a patient approach during fermentation, thriving when allowed to progress slowly and at lower temperatures. This yeast contributes to sake with a vibrant nose and a flavour profile that showcases its unique attributes. AK-1 is notably used in Akita Prefecture and has earned recognition for its role in crafting distinctive sake expressions.

These yeast strains, whether actively used or historical artifacts, each have their own set of characteristics that have influenced the development of sake over time. While some are no longer in use, they played a crucial role in shaping the sake industry and the selection of yeast strains available to brewers today.