A pint of average ale is a more sophisticated drink than a glass of fancy wine, at least as far as the yeast is concerned.

As farmers did with cattle and grains, brewers, bakers, and wine-makers “tamed” a wild microbe so that it suited their needs—producing fluffier loaves and tastier booze. Brewmasters in particular transformed beer yeast into the fermentation industry’s pet, according to two independent studies that have traced the genetic history of brewer’s yeast, the invisible ingredient that ferments ale beer, wine, and other products such as bread by transforming sugar into alcohol and bubbles.

The researchers looked at the DNA of yeast strains used to make a variety of fermented products, including ale and wine. They found that the DNA of beer-fermenting strains is remarkably different from that of wild strains. In fact, beer yeasts are so specialized in fermenting malt and so accustomed to living in breweries that they are no longer able to survive in nature.

Wine yeasts’ DNA, instead, is more similar to that of wild variants. “We compare [wine yeasts] to cats: they’re somehow domesticated—they clearly got better at fermenting wine—but they’re still okay living in the wild,” said Kevin Verstrepen, an associate professor at the University of Leuven and senior author of one of the studies. “Beer yeasts are more like dogs: they are completely tamed.”

Verstrepen thinks these differences have to do with the way the two drinks are produced. “Wine is made once a year, while beer is produced all year round,” he said. Traditionally, after the harvest of the grapes, wine yeasts were grown in grape juice for about one month, but for the rest of the year they had to survive in nature—on grapes’ skin in vineyards.

Beer yeasts, instead, were continuously kept in breweries where brewmasters provided abundant food in the form of sugar. “Historically, breweries were running ahead of wineries because brewers were recycling their yeasts throughout the year and constantly selecting the best batches,” Verstrepen said.

Although the first evidence of beer production dates back 5,000 years ago, Verstrepen explained that brewers started to consciously select their best yeasts around the late 1500s, when beer production moved from private houses to pubs and monasteries.

At the end of the beer-making process, yeast cells that have eaten all the sugar and produced all the alcohol sink to the bottom of the fermenter and form a sediment. “What happened—we know this from old brewing books—is that brewers learned to collect this sediment and put it into a new batch of beer fermentation,” Verstrepen said.

By repeating this process with the yeasts that produced the best beers, brewers were allowing them to continually grow in, and therefore adapt to, the brewery environment. “This happened way before the discovery of microbes. It was really based on the brewers’ gut-feeling and craft,” Verstrepen said.

Verstrepen and his team analyzed the DNA of over 150 strains of yeast used to produce ale beer, wine, bread, saké, and bioethanol—a fermented alternative to gasoline. In an article published in the journal Cell , the researchers reported that all these industrial strains derive from a few wild ancestors. Industrial yeasts differ from their “parents” in that they show signs of domestication, or adaptation to living in a man-made environment such as a fermenter.

Similar results have been obtained by geneticists led by José Paulo Sampaio at the Nova University of Lisbon, who analyzed the DNA of 90 industrial yeast strains. Their findings are detailed in the journal Current Biology .

Both teams found that the domestication signatures are most evident in beer yeasts’ DNA. For example, these yeasts have multiple copies of the genes that allow them to feed on maltose, one of the sugars they use to produce alcohol. “Yeasts sometimes come across maltose in nature, so they are able to eat it, but for beer yeasts, maltose is the main part of their diet,” Verstrepen said. “The extra copies of the genes involved in maltose uptake and metabolism allow [yeasts] to eat more quickly and do their job faster.” Yeasts that ferment other products such as wine do not have these extra copies.

The scientists also found that beer yeasts do not produce a compound that wine yeasts do—one that smells like smoke or cloves. “This is an aroma compound that most wild yeasts would make, but in beer it is generally not desirable, so brewers must have selected natural variants that didn’t make this compound,” Sampaio said.

“These studies lay the groundwork for some really interesting applied science,” said Scott Britton, research & development scientist at Duvel Moortgat Brewery, who was not involved in the research. “They show how [yeast] strains have been manipulated by humans over time to help the brewing industry in terms of fermentation efficiency and flavor,” he said. According to Britton, knowing the genes that are important for yeasts to make tastier beer, faster, could help modern brewers improve their products.

Peter Bouckaert, brewmaster at New Belgium Brewing Company, believes that brewers can now use this knowledge to breed the best strains and screen their offspring for desirable features, such as better aromas or quicker fermentation.

For this reason, Bouckaert thinks that DNA analysis should be complemented by studies that look at which flavors and compounds are found in the final product. “[What] is useful to me is analyzing if what I want to be present in my beer is indeed present,” he said.

Vicente Pelechano, a yeast geneticist at the Karolinska Institute who was not involved in either study, thinks more research is needed to understand the yeast traits that are meaningful to brewers. “The association between a gene and a specific trait is not straightforward in many cases,” he said.

Most traits are determined by a series of factors, both genetic and environmental, Pelechano said. In humans, for example, traits like height and weight do not depend on a single gene but on a combination of multiple genes and environmental cues. Pelechano said the same might be true for traits such as aroma production in yeast.

Nevertheless, Pelechano thinks these studies represent a useful resource for the brew community. “They provide a reference chart that will allow [brewers] to focus on the most desirable genes and decide which yeast strains they want to mix.”

Verstrepen said several companies have approached him already. “[They’re] mostly beer brewers asking if we could make better yeasts for them,” he said. “[What we do] is just breeding, there is no genetic modification involved.”

Verstrepen added that other labs worldwide are investing in producing superior wine yeasts. “Traditionally, wine yeasts have been lagging behind, but wine-makers are trying to close the gap.”

Half of Verstrepen’s lab is now involved in applied research for influencing yeast traits that brewing companies care about. “I think for brewers these are gonna be fun times where they can experiment and create new beers with different flavors,” Verstrepen said.

Photo credit: Wagner T. Cassimiro "Aranha"/ Flickr (CC BY 2.0)

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