OnTap Magazine

28 | Winter 2024 | ontapmag.co.za Lagers, or lager beers, belong to a class of beers offering a world of flavours and diversity beyond common knowledge. Most consumers are familiar with the relatively neutral, pale, medium alcohol level, crystal clear and mildly bitter versions. However, there is a vast range of flavours within the lager category. Pale lagers are often considered to be the most drinkable and therefore the most consumed all around the world, alongside regional variations and very strong branding. But lager beers exhibit wide variation of characteristics comparable to ale beers, including colour, hoppiness, maltiness, bitterness levels, body, etc. Amongst the most traditional parameters of lagers are the fermented flavours, which tend to be less intense over time. This parameter changes with new craft lagers, and it is a direct consequence of the chosen yeast and fermentation process. What defines a lager beer? If it’s not solely flavour characteristics that define what a lager beer is, what does? The answer lies with the yeast specie used to ferment it. While ale beers are fermentedwith wide range of Saccharomyces cerevisiae (S. cerevisiae) strains, lager beers are all fermented by Saccharomyces pastorianus (S. pastorianus) , a bottom fermenting yeast. Bottomfermentation isoftenused todescribe lager fermentation. Our ancestors, without understanding the phenomenon, used to collect yeast from the top of open fermenters. Doing so, a specific phenotype that rises at the end of fermentation was selected: top fermentation (ale yeast). To the contrary, lager yeast is defined by another phenotype: yeast that settles down at the end of fermentation. (It is worth noting however, that today this distinction doesn't necessarily hold true due to advancements in brewing techniques and yeast management.) Lager yeast is relatively recent in evolutionary history compared to S. cerevisiae. With traces of fermented grain dating over 10,000 years, S. cerevisiae has been part of the human diet for millennia. As a result, numerous domestication events allowed its phenotypes to evolve. Among others, maltotriose utilisation has been increased and phenol production lowered to be used for beer production: both being important and differential flavour aspects in lagers. S. pastorianus is actually a hybrid yeast. For a significant period, only one parent of this hybrid was known: S. cerevisiae . More recently, the puzzle was solved with the discovery of Saccharomyces eubayanus ; the second parent according to today’s microbial evolution theory. While the exact details of the hybridization event remain uncertain, extensive research has shed light on the process. Most likely, the new hybrid was born when S. cerevisiae and S. eubayanus bred in a brewery environment. A plausible scenario suggests that this breeding may have taken place during fermentation in the cold caves of Bavaria during the 15th century. Cryotolerance, which is the ability to maintain physiological and genetic stability at low temperatures, played a significant role in the selection of the lager yeast species. Lager yeast was favoured for its capacity to ferment at low temperatures, unlike ale yeast, which struggles to complete fermentation below 16 - 18 °C. Lager yeast can effectively achieve final attenuation at temperatures lower than 11°C. In Czech Republic, it’s not uncommon to transfer beer in maturation tanks when around 3 - 4 °C (when attenuation has only reached 73-75%). This extended fermentation process may take an additional three months, but it will not stop until it’s over. Apart frombeing cryotolerant, S. pastorianus yeast strain exhibits characteristics such as medium-high attenuation, good flocculation and sedimentation properties, alongside being phenolic off flavour (POF) negative. Compared with ale yeast, lager strains have lower genetic diversity. Lastly, lager yeast is known, apart from exceptions, to be very neutral in its fermentative flavour formation. S. pastorianus does not produce noticeable amounts of higher alcohol (fusel alcohols) and fruity esters compared to S. cerevisiae . But what is neutrality in beer? A brewmaster can make the perfect wort in the brewhouse, however, the wort produced will not be a tasty beverage. Wort is heavy, not refreshing, and full of undesired aldehydes. Only a beer yeast can remove these aldehydes, and increase the freshness and drinkability – in a word make a good beer. To that end, lager yeast is not neutral at all (nor is ale yeast). Lager yeast reveals the hidden potential of the raw material used and unveils all the effort of the brewmaster who has worked so hard to make the perfect beer. Diversity of the lager beer styles? When thinking about the vast diversity of lager beer, one common feature comes to mind: balance. Unlike certain modern versions of craft ale beers, the soul of most lagers is finding the perfect equilibrium between bitterness, sweetness, drinkability, malt character and fermentative flavours. Finding the perfect strain for eachbeer style alongsidebrewery specificity is ofmajor importance. Pilsner is the most iconic style of what is considered a premium lager. A Pilsner typically offers a crisp and refreshing taste with Gilles Goemaere (Technical Sales Support Manager) and Gabriela Montandon , PhD (Fermentis Academy Sensory Analysis Manager) ADV E RTOR I A L LAGER BEER A WHOLE WORLD OF POSSIBILITY