Scientists have now uncovered the DNA of the organism that sets lager beers apart from ales.
History of lagers and ales
While ales are traditionally made with the ubiquitous Saccharromyces cerevisiae—commonly known as baker’s yeast because of its use in making breads—lager-style beers are made from domesticated hybrids of different yeast species. Compared to ales that have been brewed for millennia using relatively pure strains of yeast, lagers are a recent invention, originating in 15th century central Europe. Typically, lagers utilize yeasts that could ferment at lower temperatures, a process that gives them their distinctively crisp taste. Lagers enjoy a whopping 94% share in the world beer market today.
Lineage of lager beers
Not until recently, lagers were thought to contain a single species of yeast called the Saccharomyces pastorianus syn. S. carlsbergensis. It was only in 2008 that it was proposed that a hybrid of S. cerevisiae and an unknown parent was the prime organism.
We know now that the unknown parent is called Saccharomyces eubayanus, a type of wild yeast found in Patagonia, and whose genome can answer questions to its evolution into an industrial lager ingredient. The sequencing of this genome allowed the scientists to trace the genealogy of lager yeasts to two separate family lines—Saaz and Frohberg—based on their area of origin. They concluded that both these lineages originated from different sources of the ale yeast, S. cerevisiae, that separately hybridized with similar strains of S.eubayanus. Of these, the Saaz strains are now rarely used to make beer due to some undesirable properties, which could also be explained by the DNA sequence.
Why did the lager yeast evolve so rapidly?
In addition to tracing the distinct strains of yeast used to make lager, the scientists also wanted to use the genome sequence to study whether the lager yeast displayed unmistakable signs of domestication. Such signs are also seen in domesticated plants and animals, wherein some of their genes selectively undergo rapid evolution compared to their wild counterparts, thus allowing them to thrive in their environment. When compared to the pure S.eubayanus, today’s lager yeast has indeed evolved significantly in specific sets of genes, specifically those involved in fermentation and sugar metabolism. It is believed that years of brewing may have led to the selective evolution of genes that are key to making this beer.
