Traditional Norwegian Kveik Yeast: An Ancient Sister Group to Domesticated Saccharomyces cerevisiae

Kveik is the common name of yeast that has been used in traditional farmhouse brewing of western Norway for generations. Its fast fermentation, increased flocculation, temperature tolerance, and rich flavor profile have led to growing interest in recent years. Previous genetic analyses have shown that kveik forms a distinct group within the Saccharomyces cerevisiae tree and placed its origins within the Beer I clade of industrial brewing yeasts, although with signs of mixed ancestry. In this study, we revisited the phylogenetic position of kveik within the S. cerevisiae tree. We searched for traditional farm breweries in western Norway and collected ten samples of potential kveik yeast. Using Illumina whole genome shotgun sequencing, we reconstructed the phylogenetic tree of kveik based on de novo genome assemblies and variant calls of our new kveik samples, along with published wild and domesticated S. cerevisiae strains. We calibrated and used sequential computational experiments at different thresholds to determine the most probable phylogenetic position of kveik yeast. Previously sequenced kveik genotypes form a clade with our new samples clustering partially by place of origin. Our results indicate that kveik is indeed a compact clade within S. cerevisiae with significantly reduced polymorphism compared to common brewing yeasts and wild strains. Contrary to what was previously thought, our analyses support a more ancient divergence of kveik and place it closer to the root of the S. cerevisiae tree. In conclusion, our genetic analyses suggest that kveik is a unique and ancient yeast group, distinct from other domesticated S. cerevisiae strains. Considering a possible far east origin of kveik yeast, the apparent endemism to western Norway remains as a big paradox These findings have important implications for the understanding of yeast domestication and the use of kveik in modern brewing practices.