10/10/2014
We know that yeasts produce the molecules that make ales and lagers so aromatic. But why do they do it?Whether you're catching a whiff of banana from a tall glass of Hefewiezen or enjoying the subtle floral aromas in your favorite American IPA, you have yeast to thank for it. Yeast imbues beer with aromatic molecules that account for a great deal of its final flavor; almost all wild yeasts create these pleasant smells and tastes as they eat.Yet even though we know yeast is the reason beer tastes so good, we don't know exactly why it does it. But in a new study, a team of scientists led by Kevin Verstrepen, a yeast geneticist at the Flanders Institute for Biotechnology and the Belgian University of Leuven, has showed why these tiny microbes make the flavors we savor.In a new paper in the journal Cell, the scientists detail the results of four experiments on yeast. It turns out that for yeast, producing these delicious aromatic molecules is a bit like hailing a taxi. The smell lures in wandering flies, to which yeasts hitch a ride so they can disperse throughout nature.Serendipity and Dirty Lab Equipment"This theory actually came about entirely by accident," Verstrepen says. Fifteen years ago, working on his Ph.D., he was investigating the gene that controls the production of these aromatic molecules in yeast. "At one point on a Friday night, I was in hurry to get to the bar and didn't clean up my experiment as well as I should have," he says.He accidentally left out three flasks of yeast. "One flask had a mutant strain of yeast that produced 100 times more [of these aromatic molecules], one flask contained normal yeast, and a third had a yeast with this aroma gene partially knocked out," Verstrepen says."When I returned Monday morning, I found that somehow fruit flies had gotten into the lab," he says. And realizing that he had unwittingly set up an experiment, he wrote down the results. "Fifty flies drowned in the mutant flask, two drowned in the flask of normal yeast, and the flask with the [nonaromatic] yeast didn't have any," he says. "You don't have to be a genius to start to draw some conclusions from that."All these years later Verstrepen teamed up with a group of fly neurobiologists to test his idea. They did it in four parts."The Arena"1. In the first of Verstrepen's experiments, the scientists identified and picked out a particularly potent aroma-producing yeast strain. They then knocked out the gene called ATF1, which is responsible for creating th …