“I’ll take the mutant sake with the extra ornithine,” said no one ever. But thanks to research out of Japan, we might soon be able to order a bottle of the rice wine in a somewhat similar way.
There’s a paradox in brewing. You want the yeast to eat sugar and create ethanol (what most of us call alcohol), but you also want them to not die as the liquid they’re in starts to build more alcohol. So brewers look for ethanol-tolerant yeast.
“We wanted to obtain sake yeast strains with improved ethanol tolerance,” first author on a paper describing the research, Masataka Ohashi. “During sake fermentation, the yeast is exposed to high concentrations of ethanol, which impedes yeast cell growth, viability, and fermentation. Increased ethanol tolerance in sake yeast strains could improve ethanol production and reduce fermentation time.”
In seeking a more ethanol-resistant yeast, researchers from the Nara Institute of Science and Technology and the Nara Prefecture Institute of Industrial Development in Japan turned to mutant yeast strains that create high levels of ornithine. Ornithine is an amino acid not involved in protein formation, but one that acts as the precursor to two amino acids that are: proline and arginine. It has been shown to boost energy and athletic performance and might also—of all things—help minimize hangovers.
To develop yeast strains that produced more ornithine, the researchers allowed a common yeast to mutate naturally to overcome market aversion to genetically modified products.
“We previously constructed self-cloning industrial yeast strains that accumulate proline to increase ethanol tolerance and productivity of yeast,” said Prof. Hiroshi Takagi, corresponding author on the paper that appeared in Metabolic Engineering. “But those yeasts have not been yet acceptable to consumers because they’re considered to be genetically modified, even though a self-cloning yeast has no foreign genes or DNA sequences—they only have yeast DNA.”
The researchers were able to isolate a yeast strain that manufactured ten times the amount of ornithine made by a yeast strain commonly used to brew sake, while the sake itself contained 4-5 times ornithine than usual.
Whether or not the sake will convey energy to its consumers remains to be seen. Still, the researchers say their ethanol-tolerant yeast can be applied to other brewing categories such as beer, as well as to the production of ornithine dietary supplements.
“The yeast is reliable and safe in food production, and thus the development of novel strains that overproduce ‘functional amino acids’ such as ornithine, proline and branched-amino acids, would greatly contribute to food-related industries,” said Ohashi.