Beer has a distinct smell. New research suggests there's a reason why this popular alcoholic beverage smells this way: to attract fruit flies.

The common brewer's yeast is responsible for the beer's most prominent odor, and these produce chemicals that mimic the aroma of a ripening fruit that attracts pesky little flies. While flies can be an annoyance for brewers, they actually benefit the yeast as the flies disperse the yeast into the environment.

In a new study published in the journal Cell Reports on Oct. 9, Kevin Verstrepen from the VIB Laboratory of Systems Biology in Leuven, Belgium and his colleagues conducted an experiment to see how flies would respond to yeast when the alcohol acetyl transferase (ATF1) yeast gene, which is responsible for aroma synthesis, is removed. They found that flies were not attracted to the mutant yeast cells and this too has unwanted implications on the yeast.

When the flies land on the fruity non-mutated yeast, they unknowingly pick the yeasts on their legs and disperse them. The flies, however, were not attracted to the aroma-mutated yeast. As a result, the yeast was not as much dispersed as the smelly yeast.

"Deletion of ATF1 alters the olfactory response in the antennal lobe of fruit flies that feed on yeast cells," the researchers wrote. "The flies are much less attracted to the mutant yeast cells, and this in turn results in reduced dispersal of the mutant yeast cells by the flies."

Verstrepen said that the mutually beneficial relationship of flies and yeast may have existed for millions of years. The flies eat yeast for protein, with the scent serving as their guide to the source. The yeast cells then benefit from the fruit flies as they are dispersed to new places.

The researchers explained that because the yeast does not have the capability to move around on its own, it may have developed the strategy so it can be transported from nutrient-poor environments to nutrient-rich habitats such as ripe fruit or rotting trash that fruit flies incidentally always frequent.

It likewise appears that humans also benefit from the volatile compounds that give beer its pungent smell because of the compounds' role in the flavors of beer and wine.

"Recent research shows that the choice of a particular yeast strain or variety explains differences in taste between different beers and wines," Verstrepen said. "In fact, yeasts may even be responsible for much of the 'terroir,' the connection between a particular growing area and wine flavor, which previously often was attributed to differences in the soil."

TAG Beer, yeast, Wine, flies, Brewers, Symbiosis

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