We have fruit flies to thank for beer's familiar smell, according to new research.
The most prominent odors released by beer are produced by common brewer's yeast, which evolved the aroma to attract fruit flies. The flies, in turn, benefit yeast by dispersing its cells into the environment.
Faces of Bees, Flies and Friends: Photos
"Two seemingly unrelated species, yeasts and flies, have developed an intricate symbiosis based on smell," researcher Kevin Verstrepen of KU Leuven and VIB in Belgium said in a press release. "The flies can feed on the yeasts, and the yeasts benefit from the movement of the flies."
A paper on the unlikely duo - beer and flies - is published in the latest issue of Cell Reports.
Verstrepen had a light bulb moment 15 years ago while studying how yeast cells contribute to the flavor of both beer and wine.
He discovered that yeast cells produce several pleasant and appetizing aroma compounds similar to those produced by ripening fruits. Like fruit, the yeast uses these tempting smells to lure in beneficial others. One yeast gene in particular, alcohol acetyl transferase (ATF1), was responsible for most of the volatile chemicals.
Video: Beer: Healthier Than Running!
Verstrepen recalled, "When returning to the lab after a weekend, I found that a flask with a smelly yeast culture was infested by fruit flies that had escaped from a neighboring genetics lab, whereas another flask that contained a mutant yeast strain in which the aroma gene was deleted did not contain any flies."
The years passed, but he never forgot that moment.
For the recent study, he teamed up with fruit fly neurobiologists Emre Yaksi and Bassem Hassan. The researchers used a combination of molecular biology, neurobiology and behavioral tests to show that loss of ATF1 changes the response of the fruit fly brain to a whiff of yeast.
As predicted from the earlier work, mutant yeast cells were a turnoff to the flies. This was bad for the yeast too, since the altered yeast wasn't dispersed much by the flies.
What Did Iron Age Beer Taste Like?
The research as a whole suggests that the lives of microbes and insects may be intertwined, with each evolving various traits, including smell, to benefit both parties.
The scientists also examined the flies themselves and found that the tiny insects always gravitate toward fragrant yeast, based on yeast remains found in and on the flies' bodies.
Beer and wine connoisseurs often wax poetic when characterizing the smells of these popular beverages, but the next time you get a whiff of beer, think of fruit flies and their contribution to this drink's characteristic odor.
Photo: A frosty mug full of beer. Credit: Len Rizzi, National Institutes of Health