A Large Set of Newly Created Interspecific Saccharomyces Hybrids Increases Aromatic Diversity in Lager Beers

Abstract

Lager beer is the most consumed alcoholic beverage in the world. Its production process is marked by a fermentation conducted at low (8 to 15°C) temperatures and by the use of Saccharomyces pastorianus, an interspecific hybrid between Saccharomyces cerevisiae and the cold-tolerant Saccharomyces eubayanus. Recent whole-genome-sequencing efforts revealed that the currently available lager yeasts belong to one of only two archetypes, "Saaz" and "Frohberg." This limited genetic variation likely reflects that all lager yeasts descend from only two separate interspecific hybridization events, which may also explain the relatively limited aromatic diversity between the available lager beer yeasts compared to, for example, wine and ale beer yeasts. In this study, 31 novel interspecific yeast hybrids were developed, resulting from large-scale robot-assisted selection and breeding between carefully selected strains of S. cerevisiae (six strains) and S. eubayanus (two strains). Interestingly, many of the resulting hybrids showed a broader temperature tolerance than their parental strains and reference S. pastorianus yeasts. Moreover, they combined a high fermentation capacity with a desirable aroma profile in laboratory-scale lager beer fermentations, thereby successfully enriching the currently available lager yeast biodiversity. Pilot-scale trials further confirmed the industrial potential of these hybrids and identified one strain, hybrid H29, which combines a fast fermentation, high attenuation, and the production of a complex, desirable fruity aroma. With an annual production exceeding 1.97 billion hectoliters a year, beer is the most-produced fermented beverage in the world (1). The vast majority of currently produced beer is classified as either ale or lager beer, each type being produced by a unique fermentation process (2). Specifically, ale beer production uses the common brewer's yeast Saccharomyces cerevisiae and relatively high fermentation temperatures (typically 18 to 25°C) (2-5).In contrast, lager beer (with Pilsner beer as the most popular and commonly known type of lager beer) is fermented at lower temperatures (5 to 15°C), followed by a period of cold storage (lagering), which is a traditional practice vital for the beer's characteristically clean flavor and aroma. Lagers are not fermented by S. cerevisiae but by the closely related species Saccharomyces pastorianus (formerly known as Saccharomyces carlsbergensis), which combines the desirable fermentation characteristics of S. cerevisiae with the cold tolerance of its other parent, S. eubayanus (6). Lager beer currently accounts for more than 90% of the global beer market but has a much more recent origin than ales. The lager beer production process was developed in the 16th century in Bavaria (Germany), where brewing was only allowed during wintertime to minimize the microbial spoilage of beer. Later, in the 19th century, the advent of refrigeration enabled lager brewing throughout the whole year (2, 3, 7).Several recent studies have focused on analyzi...

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

“…The development of hybrids has proven to be a powerful approach to generate novel yeast variants with enhanced characteristics for lager beer (4,7,31). This is very important for the brewing industry because, as recently demonstrated (32), the available commercial strains have been cultivated over the years, suffering an intense domestication process that led to a strong industry-specific selection for many important traits (stress tolerance, sugar utilization, flavor production, etc.).…”

“…Saaz-type strains produce lower concentrations of aroma compounds, like ethyl acetate, 3-methylbutanol, and 3-methylbutyl acetate, than the more aroma-rich Frohberg yeasts (6). This phenotypic difference has resulted in the diversified and differentiated aromas of lager beers in the market and explains the preference for Frohberg-type lager yeasts over Saaz-type lager yeasts in the beer industry (7).…”

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

“…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). Kvasinky Saaz vykazují větší toleranci k nízkým teplotám.…”

“…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). Saaz yeasts have greater tolerance to low temperatures, this property being affected by the gene KEX2 from S. eubayanus.…”

Saccharomyces and Non-Saccharomyces Starter Yeasts

“…The production and increase in the aroma compounds through biological methods exploits the metabolic pathways of the yeast for the promotion of the so-called biolavor. This approach includes microbial bioconversion of the lavor precursors, use of strains that produce the required compounds, and genetic modiication of the yeast [35]. In this regard, although still poorly investigated in the brewing sector, the use of nonconventional yeast might enhance the analytical and aromatic proiles of the inal product and reduce the alcohol content [36].…”