New yeast strains can produce untapped flavours of lager

Different yeast strains fed the exact same sugary diet will create different flavours of beer. Yet lager-fanciers have been short-changed—there are only 85 strains of lager yeast, compared with 358 strains for ale. If a team led by Jennifer Molinet and Francisco Cubillos at the University of Santiago, in Chile, get their way, though, new types of lager may soon arrive, with completely different aromas and flavours from anything currently on tap.

Lager yeast are hybrids, a combination of Saccharomyces cerevisiae and Saccharomyces eubayanus. S. cerevisiae is the old faithful of brewers and bakers—a central ingredient in wines and breads, as well as beers. S. eubayanus is more specialised, thriving in chilly environments.

Strains of S. eubayanus and S. cerevisiae first crossed over somewhere in Germany more than 400 years ago. Ever since, lager yeast have been carefully bred and selected to maximise their taste, speed of fermentation and durability. To this day all extant lager strains are derived from this original hybrid, and belong to one of only two genetically distinct groups, Saaz and Frohberg, named after a Czech town and a German brewery, respectively.

For centuries these were thought to be the limits of the lager universe. But in a paper in PLOS Genetics, Dr Molinet, Dr Cubillos and their colleagues unveiled new hybrids of S. cerevisiae and S. eubayanus. Such hybrids would have been impossible to create before 2011, says Dr Cubillos. That was when a different team of researchers uncovered new strains of S. eubayanus in the bark of Southern beech trees in Patagonia. Dr Molinet’s interest was first sparked by the yeast’s ability to survive the cold, harsh climes of Tierra del Fuego, the region’s southernmost tip. Only later did she think of making new lager hybrids.

The first hybrid that Dr Molinet and colleagues created in 2021 was a failure. It was no better at converting sugars into alcohol than its parent strains. That was no surprise—today’s top lager yeasts have benefited from centuries of careful breeding. Undeterred, the researchers artificially accelerated evolution. Over the next seven months or so, the team created hundreds of generations of lager yeast, each time selecting the ones with the most desirable traits for making a delicious brew. They soon noticed that yeast that inherited mitochondria (the energy-producing part of cells) from S. eubayanus rather than S. cerevisiae did particularly well. The researchers suspect that since these mitochondria come from the cold-loving S. eubayanus, they are better suited to the brewing conditions necessary for lager.

After 250 generations, the researchers found that improvements plateaued. The final hybrid, called H3-E, was a more effective fermenter than any of its ancestors. It was also hardier and more flavourful. Compared with the citrusy taste of a commercial lager, the H3-E hybrid is spicy with hints of clove. (Even ale drinkers might be tempted.) When the researchers presented their work at a microbiology conference in Chile last year, they did so alongside 500 litres of their brew. It was a hit. “People were unhappy when it ran out," says Dr Cubillos. Breweries in Chile have since used their hybrid for local competitions and to sell to customers in limited-edition batches.

Don’t try to order it from a nearby pub quite yet, though. Commercial lager yeast typically ferments in seven days, half the time the new hybrid needs. That will slow down large-scale production. But Dr Cubillos and his team are refining their technique, and are optimistic about the future. That calls for a drink.

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