Abstract 

Human activity has resulted in the domestication of Saccharomyces cerevisiae yeasts specifically adapted to beer production. While there is evidence beer yeast domestication was accelerated by industrialization of beer, there also exists a home-brewing culture in western Norway which has passed down yeasts referred to as kveik for generations. This practice has resulted in yeasts which are typically highly flocculant, POF-, and exhibit a high rate of fermentation, similar to other lineages of domesticated yeast. Additionally, these yeasts are highly temperature tolerant due to the traditional practice of pitching yeast into warm (>30 ºC) wort. Here, we characterize Kveik yeasts from 9 different Norwegian sources via PCR fingerprinting, phenotypic screens, lab-scale fermentations, and flavour metabolite analysis using HS-SPME-GC-MS. Genetic fingerprinting suggests that kveik yeasts form a lineage distinct from other domesticated yeasts. We confirm that kveik yeasts display hallmarks of domestication like loss of 4-vinylguaiacol production and high flocculation, and show that many kveik have superior thermotolerance, ethanol tolerance, fermentation rate, and flavour metabolite production, suggesting a broad industrial potential for this group of yeasts.

Introduction

It is now clear that, much like with livestock and crops, human activity has resulted in the domestication of Saccharomyces cerevisiae yeasts specifically adapted for beer production. Recently, it has been shown that present-day industrial beer yeasts have originated from a handful of domesticated ancestors, with one major clade comprising the majority of German, British, and American ale yeasts, and another clade more closely related to wine yeasts which does not have geographic structure \cite{Gallone_2016}. In general, it appears that human selection of yeasts over the span of centuries has resulted in the evolution of mechanisms to efficiently ferment wort sugars such as maltose and maltotriose via duplications of MAL genes, as well as frequent nonsense mutation in genes responsible for production of 4-vinyl guaiacol (4-VG) such as PAD1 and FCD1, which in wild yeasts result in often undesirable phenolic off-flavour (POF) \cite{Brown_2010}\cite{Gallone_2016} 
 (Brown, Murray, & Verstrepen, 2010; Gallone et al., 2016; McMurrough et al., 1996; Steensels & Verstrepen, 2014; Gonçalves et al., 2016).
 
Regardless of the region of origin, yeast was maintained and domesticated by reuse (repitching) as well as sharing amongst generations of brewers, resulting in many of the modern beer yeasts used in the present day (Gallone et al., 2016; Gibson, Lawrence, Leclaire, Powell, & Smart, 2007; Libkind et al., 2011; Steensels & Snoek, 2014). It must not be assumed, however, that the domestication of beer yeasts occurred solely within the confines of industrial breweries, as there were farmhouse brewing traditions predating the industrialization of beer across northern Europe[1]  (Nordland, 1969; Räsänen 1975). However, the growing industrialization of Europe coupled with convenient commercial yeast availability has abolished traditional home-brewing in the vast majority of cases, resulting in the loss of regionally unique, domesticated yeasts in the process (Nordland, 1969; Räsänen, 1975; Salomonsson, 1979[2] ).