brewer's yeast

Who knew that flies have the same penchant for beer as we do? Scientists have only recently realized that for the last million or so odd-years, those pesky flies hovering over brewing beer are actually responsible for dispersing the yeast, and thus creating the beer that we have come to enjoy.

The chemicals that common brewer’s yeast (S. cerevisiae) produces almost exactly mirrors the same scent of ripening fruit, the same smell that lures flies. Flies consume yeast for protein, and subsequently the flies disperse the yeast to new places. Yeast isn’t capable of moving on its own, therefore it must rely on the flies’ ability to transport it from nutrient-weak habitats to nutrient-rich environments.

The aroma gene that attracts flies to yeast is called alcohol acetyl transferase (ATF1). Kevin Verstrepen, a researcher from the VIB Laboratory of Systems Biology in Leuven, Belgium, had been contemplating flies and their affect on brewers yeast for nearly two decades. Recently, he and his colleagues decided to test whether or not flies would react the same way to yeast if they removed ATF1. They conducted the test by filling one flask with a typical, pungent brewer’s yeast culture and another with a mutant yeast strain that didn’t contain the aroma gene. Verstrepen and his team observed the two flasks for two days and discovered that no flies were attracted the mutant yeast strain, whereas the brewer’s yeast culture contained a swarm of flies. Without flies transporting the yeast, the beer isn’t able to cultivate properly.

“These preliminary results suggest that aroma production is not restricted to S. cerevisiae and may be a much more general theme in microbe-insect interactions. Deletion of ATF1 alters the olfactory response in the antennal lobe of fruit flies that feed on yeast cells,” said the researchers. “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’s studies are inspiring a slew of connections between insects and aroma-producing yeasts found in plants and wines. Wine flavor, which has been associated with soil production, might now be linked to the varying of yeast strains.

So the next time you lift up a glass a beer to enjoy, and a pesky fly begins to buzz around, just remember that you might not be enjoying the brew without the help of its ancestors.

(Photo courtesy of Quinn Dombrowski)