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The Secret Behind Your Favorite Coffee Could Be Yeast

Researchers find three unique strains of yeast that help ferment coffee and cacao beans and may give the treats their unique flavors

Cacao beans drying in the Dominican Republic (Owen Franken/Corbis)
smithsonian.com

Though dogs are usually considered humankind's best friend, if you really think about it, the animal that gives many people the most joy is yeast. More specifically, Saccharomyces cerevisiae is the species of yeast used for making wine, raising bread and fermenting beer. Now, new research indicates that various strains of the wonder yeast may also give different regional coffees and chocolates their distinct flavors.

S. cerevisiae actually has many more purposes beyond food and drink. Scientists use this yeast extensively in lab research because the single-celled organism has a structure similar to human cells, but reproduces very, very quickly. That’s the reason behind testing drugs on yeast, studying the genes of yeast and even sending the stuff into space.

Lizzie Wade at Science reports that when Aimée Dudley, a geneticist at the Pacific Northwest Diabetes Research Institute, decided to build a map of all the various strains of S. cerevisiae, she discovered there were gaps in the research collections with most of the southern hemisphere missing—including much of Africa, Asia, South America, and Indonesia.

Traveling to all those areas would be timely and cost prohibitive, so Dudley and her team decided to do the next best thing. Knowing that chocolate and coffee go through a fermentation process, they began buying coffee and cacao beans from around the world, culturing them for yeast.

They thought they would find similar strains of S. cerevisiae in all the samples, but that wasn’t the case. “The first really interesting thing we noticed was that they were all very different from each other,” Dudley tells Eric Smillie at Newsweek. “So a coffee strain from Colombian coffee was very similar to other Colombian strains, but it was really different from Yemeni coffee.”

The research shows that the coffee and cacao yeasts are a combination of three yeast strains, the European variation used for wine making, a variety common to Asia, and another strain from North American oak forests. Their paper, published in the journal Current Biologyshows how those strains spread and combined through the world through human migration, when people brought regional strains of yeast together both intentionally and unintentionally.

“This paper is further evidence of how intertwined the history of humans and yeast has been,” Barbara Dunn, a geneticist at Stanford tells Science. “It’s really, truly a mixture of nature and nurture.”

While the paper doesn’t directly investigate whether the yeasts impact the flavor of cacao and coffee, it’s highly likely that the microbes have a huge impact. According to Smillie, the yeast breaks down the cherry around the coffee bean and the pulp surrounding the cacao, producing “flavor precursors” that create distinctive tastes and smells when roasted.

“[We] can reliably get six different flavor profiles from the same variety of bean by varying fermentation and drying,” chocolate consultant Clay Gordon tells Newsweek. “You can get flavors that are fruity and bright or leathery and tobacco-y just by controlling the postharvest processing.”

It’s similar to what scientists have learned about the way tiny variations in yeast affect a wine’s terroir, or flavor profile that comes from the weather conditions, soil and microbes of the land where it is produced. Sarah Knight, a geneticist at the University of Aukland told Wade that each variety of yeast releases unique metabolites that affect the characteristics of wine.

“So it wouldn’t be surprising,” she says, “if these genetically differentiated populations [of yeast] are making slightly different combinations of compounds, and that may change the way that the chocolate tastes and smells.”

So raise a glass of pinot or a cup of Joe to Saccharomyces cerevisiae. Just don’t let the dog see you.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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