For centuries, lager beer has been made from the same core ingredients: malt, hops and yeast. Curious scientists wondered if they could tweak one of these components and unlock original beer flavors.

Using yeast strains found in the bark of trees in Patagonia, the researchers brewed up new hybrid yeasts that could one day lead to beers with strikingly different tastes and aromas.

Their study, published last week in the journal PLOS Genetics, showed that these hybrids can produce just as much — and in some cases more — alcohol as commercial yeast while generating unique aromas.

“All the lager beers that we drink now come from a single event from a yeast generated 500 years ago,” said Francisco Cubillos, principal investigator of the study and professor at the University of Santiago at Chile who specializes in molecular genetics. “That makes most of the lager beers quite similar.”

The birth of lager yeast, formally known as Saccharomyces pastorianus, was a happy accident that occurred about the year 1600. S. pastorianus is a hybrid yeast born in the German state of Bavaria from two yeast parents, Saccharomyces cerevisiae and Saccharomyces eubayanus. Evidence suggests that S. cerevisiae contaminated a batch of fermenting S. eubayanus, and the first generation of lager yeast was born.

Since then, humans have been domesticating lager yeast by brewing batches of beer, throwing out the varieties that made people turn up their noses and pucker their mouths in disgust, and keeping those that smelled good and went down smoothly to use as yeast sources for future batches.

The sobering reality: All that time has given rise to just 86 strains of commercial lager yeast, a number that pales compared with the 390 strains available for making ales. (Lager is the favorite beer style and includes brands such as Budweiser, Corona and Heineken.) The limited genetic diversity of lager yeast limits possible flavors.

Given that lagers make up such a large share of the beer sold around the world, the researchers wanted to figure out how to introduce new flavors to the market by emulating the birth of S. pastorianus — but this time by using yeast parents found in the Chilean Patagonia forest.

“We put [on] music and foods, and we let [the yeasts] mate,” Cubillos quipped.

Their first attempts to hybridize winery strains of S. cerevisiae with Patagonia strains of S. eubayanus resulted in yeast duds.

“They didn’t consume all the sugar present,” said Jennifer Molinet, first author on the study and a postdoctoral researcher in Cubillos’s lab when the experiment was conducted. If yeast does not eat the sugar given to it during fermentation, it does not produce the gas and alcohol needed to make beer.

So, the researchers turned to experimental evolution, a scientific technique that involved placing the lazy hybrid yeasts in fresh, sugar-filled test tubes every few days to see how their characteristics changed over time.

After 250 evolutions each, all of which unfolded during seven months, the hybrid yeasts were filled with life and consumed all the sugar given to them.

“I was so happy, and I was jumping around the lab,” Molinet said.

The hybrids possessed distinct smells that set them apart from existing lagers. Some gave off sweet aromas, while others presented spicy and clove-like notes, deviating from the fruity and citrusy smells most lagers offer.

“It’s definitely promising,” said Zach Lilla, head chemist at Advanced Analytical Research Lab, which runs tests on fermented products to assess their properties and nutritional value.

“The cool part that I really liked about [the study] is their ability to dissect the genetic characteristics of the yeast itself,” said Lilla, who was not part of the study.

As the researchers studied the hybrid yeasts they’d created, analyzing components of cells, they found that it is mitochondria — the power plants of cells — that dictate what a yeast’s properties will be.

Lilla said the finding can enable brewers to quickly assess the genetic properties of a lager yeast candidate and look for ideal characteristics, such as fast fermentation capabilities.

“A next step in this kind of work would be to perform a pilot-scale brew and make some beer,” said Christopher Curtin, an associate professor of fermentation microbiology at Oregon State University who was not involved in the study. He explained that a sensory analysis is needed to assess whether beer made outside of the lab is different from existing lagers — and in a way that is desirable to consumers.

“There can be challenges in scaling up the performance,” Curtin said. Among them: ensuring that the yeast hybrids do not produce too much hydrogen sulfide. Though the gas is a natural product of the fermentation process, most brewers try to get rid of it, because too much can make beer smell like rotten eggs.

“We need to catch up with 500 years of domestication” of commercial yeast, Cubillos said. “But we see it as an opportunity.”



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