AsianScientist (Jul. 8, 2016) – Researchers in Japan have identified a gene mutation that could potentially disrupt the brewing of the delicious Japanese rice wine, more commonly known as sake.
The research was part of an academic-government-industry collaboration involving the National Institute of Brewing (Japan), the Asahi Sake Brewing Company, the Brewing Society of Japan, the University of Tokyo, Iwate University and the University of Pennsylvania in the US. The findings were published in Bioscience, Biotechnology, and Biochemistry.
Two types of sake considered especially high-quality are called daiginjo-shu and junmai-daiginjo-shu and are often made using the yeast K1801. Whether for beer, wine or sake, different brewing yeasts create different tastes in the final product due to factors such as how the sugar-to-alcohol conversion is carried out and the types of by-products that are released.
A previously-identified mutation in K1801 is a desirable change that makes the yeast produce high amounts of a chemical called ethyl caproate, which creates a fruity taste in many varieties of high-quality sake.
However, biologists at Hiroshima University, located in the sake-brewing town of Saijo, have identified another genetic mutation that is potentially devastating for brewers because it causes a defect in how the yeast grows and divides. The risk of a ruined brew from this yeast is a liability for industrial-scale sake production, where consistent production with stable quality is essential for brewers. The research team also confirmed that K1801’s two mutations are not functionally related.
A genetically-engineered version of K1801 that had normal growth but maintained high production of ethyl caproate was also built and used to brew sake in the laboratory.
“Our small-scale brew indicated that this version of the yeast without the growth-related mutation should maintain the high quality expected of daiginjo-shu,” said Associate Professor Dai Hirata from Hiroshima University’s Department of Molecular Biology.
Hirata is the last author of the research paper and has training and experience as a sake taster, serving as an official judge at sake evaluation events.
Unfortunately, the Japanese market will not accept sake made from genetically-modified yeast. As such, the next step for the research team is to begin screening potentially thousands of K1801 yeast cells until they can find a natural mutant with only the desirable mutation.
The article can be found at: Goshima et al. (2016) Identification of a Mutation Causing a Defective Spindle Assembly Checkpoint in High Ethyl Caproate-producing Sake Yeast Strain K1801.
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Source: Hiroshima University; Photo: Pixabay.
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