With summer and baseball season approaching, it seems like a good time to ask that eternal question, “Why do flies like beer?” That’s just what entomologists at University of California Riverside did, and they came up with the answer.

In case this sounds like frivolous research to you, know that Anupama Dahanukar, whose lab conducted the research, hopes that the knowledge of how flies detect chemicals can help us better understand how taste and smell works in humans.

The first assumption was that fruit flies are simply attracted to sugars in the beer. To test that, Dahanukar’s lab planned an experiment that would give the flies a choice between beer and sugar water to see whether they had a preference. The researchers selected a pale ale for the test because pale ales have low sugar content.

This research project sounds like a graduate student’s dream—a thesis that involves beer. “I remember it was a Saturday”, graduate student Zev Wisotsky said. “I grabbed the beer at the grocery store, came into the lab, and performed the two-choice assay.” The assay forced the fruit flies to choose between a sip of beer and a sip of sugar water. The flies went for the beer.

All very good, but the researchers still didn’t know why the flies preferred the beer. “The answer, as it turns out, was quite simple,” said Dahanukar. Turns out the flies were attracted to glycerol in the beer. Glycerol is the same stuff that’s in antifreeze; it tastes sweet but it’s not a sugar. In beer, glycerol is made by yeast during fermentation.

“Taste becomes important only after the fly makes physical contact with food,” said Dahanukar. A fly first locates food sources using its odor receptors…then, after landing on food, the fly uses its taste system to sample the food for suitability in terms of nutrition and toxicity.” A receptor in the fly’s mouthparts is responsible for recognizing the good taste of beer.

The researchers went on to discover the particular gene responsible for the flies’ ability to detect glycerol. When they bred fruit flies that were missing that gene and applied the same test, the gene-less flies choose the sugar water instead of the beer. In the real world though, you’re still going to have to fight the fruit flies for your beer.

(Sources: NPR, 11/25/11; Science Daily, 11/11/11)