Lager Yeast Comes of Age

Abstract

Alcoholic fermentations have accompanied human civilizations throughout our history. Lager yeasts have a several-centurylong tradition of providing fresh beer with clean taste. The yeast strains used for lager beer fermentation have long been recognized as hybrids between two Saccharomyces species. We summarize the initial findings on this hybrid nature, the genomics/ transcriptomics of lager yeasts, and established targets of strain improvements. Next-generation sequencing has provided fast access to yeast genomes. Its use in population genomics has uncovered many more hybridization events within Saccharomyces species, so that lager yeast hybrids are no longer the exception from the rule. These findings have led us to propose network evolution within Saccharomyces species. This "web of life" recognizes the ability of closely related species to exchange DNA and thus drain from a combined gene pool rather than be limited to a gene pool restricted by speciation. Within the domesticated lager yeasts, two groups, the Saaz and Frohberg groups, can be distinguished based on fermentation characteristics. Recent evidence suggests that these groups share an evolutionary history. We thus propose to refer to the Saaz group as Saccharomyces carlsbergensis and to the Frohberg group as Saccharomyces pastorianus based on their distinct genomes. New insight into the hybrid nature of lager yeast will provide novel directions for future strain improvement.

New Lager Brewery Strains Obtained by Crossing Techniques Using Cachaça (Brazilian Spirit) Yeasts

“…The cold adaptation of lager yeast seems have been inherited from S. eubayanus part of the genome (1,6,36,37). However, we found intraspecific hybrid strains (S. cerevisiae) able to ferment malt extract at 12°C and which produced more ethanol than their corresponding parental strains.…”

“…sugar into ethanol; among them, those belonging to the genus Saccharomyces are used for bioethanol production and dominate the wine, spirits and beer industries (1).…”

“…Ale beers are produced by strains of Saccharomyces cerevisiae, but lager beers are traditionally obtained by yeast species that result from hybridization events between S. cerevisiae and other Saccharomyces species that were selected under conditions of low-temperature fermentations for beer production (3). Beyond that, lager yeast also presents another interesting feature, the ability to flocculate that leads cells to settling at the bottom of the fermentation tank, enabling easy removal and reinoculation; in contrast, ale yeast rises to the surface (1).…”

Factors Influencing the Production of Sensory Active Substances in Brewer's and Wine Yeast

“…The type Frohberg includes strains from Netherlands (Heineken, Oranjeboom and other breweries), from Denmark (except Carlsberg brewery) and from North America. These strains retained most of the genetic material of both strains (Wendland, 2014). Allotriploid strains of Saaz aren't capable of fermenting maltotriose and have a lower fermentation rate, in contrast to allotetraploid strains of Frohberg (Mertens et al, 2015).…”

“…Skupinu typu Frohberg tvoří kmeny z Holandska (Heineken, Oranjeboom a jiné pivovary), z Dánska (kromě pivovaru Carlsberg) a Severní Ameriky. Tyto kmeny si ponechaly většinu genetického materiálu obou kmenů (Wendland, 2014). Allotriploidní kmeny Saaz nejsou schopny, na rozdíl od allotetraploidních kmenů Frohberg, fermentovat maltotriosu, což způsobuje nižší míru fermentace (Mertens et al, 2015).…”