London: Beer lovers, rejoice! Lager beers could soon have as many different flavours as real ale after scientists cross-bred yeast resulting in hundreds of new strains. Unlike ales, lager beers differ little in flavour. But now, by creating new crosses among the relevant yeasts, researchers have opened up new horizons of taste.
The relative uniformity of flavour among lagers turned out to result in significant part from a lack of genetic diversity among the yeasts, researchers said. Genetic studies showed that lager yeasts had resulted from just two crosses between the parent yeasts, Saccharomyces cerevisiae, and S eubayanus.
The problem was that the two yeast species are so different as to make successful crosses rare. “We figured that if we could create more crosses between S cerevisiae and S eubayanus, we would perhaps produce a set of more diverse lager yeasts, which could yield more diverse lager beers,” said Kevin Verstrepen, Professor in Genetics and Genomics, University of Leuven.
The researchers did their best to optimise growing conditions, hoping to encourage mating between the yeasts. To this end, they experimented with different temperatures and growing media. “We were able to get some serious sexual action between our yeasts, which resulted in hundreds of new lager yeast strains,” said Verstrepen, also director of the VIB lab for Systems Biology in Belgium.
But of 31 new strains that they tested in small scale beer fermentations, only ten performed reasonably well in terms of speed of fermentation, and flavor. They then tested the four best of these in full scale fermentations.
“Two were magnificent. They fermented more quickly than the commercially used reference lager yeast that we compared them to, and they produced really nice flavours,” said Verstrepen.
“We found that the different lager yeasts that we created showed very different aroma profiles compared to today’s commercially available lager yeasts,” said Stijn Mertens, lead author of the research paper published in the journal Applied and Environmental Microbiology.
“This means that it now becomes possible to make lager beers that, like ale beers, are more different from each other, and this without the need to extensively change the production process,” said Mertens.
Lager beers are fermented with S pastorianus, which is a hybrid between S cerevisiae and S eubayanus, at temperatures generally between 8-15 degrees Celsius. They also have a lower alcohol content, 4-5.5 per cent by volume. Ales are fermented by S cerevisiae, at higher temperatures – usually between 15-25 degrees Celsius, and they tend to be stronger than lagers.