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] )
.