Troels Prahl, a brewer and microbiologist at White Labs, a yeast distributor in San Diego, Calif., sits at his company’s tasting room bar with four half-pints of beer. He describes each between thoughtful sips.
The first has a malty backbone and a crisp body of raspberry, rosemary and banana, he says; the second, a waft of white raisin and final bite of olive brine; the third flows thick and smooth like a classic English ale; and the fourth is perfumed with a dry and subtle blend of nutmeg and fresh straw.
The beers’ colors are as varied as their flavors, ranging from cloudy gold to clear amber. Yet with the single exception of the yeasts used to ferment them, Prahl explains, they are all the exact same brew. After thousands of years of unwitting domestication, brewing yeasts – the microorganisms that ferment a brewer’s tepid slop of grain, water and hops into beer – are as diverse as the beer they make.
And now two research teams, from White Labs and a Belgian genetics laboratory, are mapping out their sprawling genealogy, creating the first genetic family tree for brewing yeasts and the beers they make. The laboratories have sequenced the DNA of more than 240 strains of brewing yeasts from around the world. Alongside samples from breweries like Sierra Nevada, Duvel Moortgat and Stone, “we’ve thrown in a few wine, bakers, bio-ethanol and sake yeasts to compare,” said Kevin Verstrepen, director of the lab in Belgium.
By getting a line-by-line reading of the 12 million molecules that make up the DNA of each yeast, Verstrepen said, the researchers will be able not only to tell how closely related two yeasts are (is Sam Adams’ closer to Stone’s, or Sierra Nevada’s?) but to answer other important questions: which breweries started with the same strains of yeasts, how these organisms evolved over time and, of course, how all of it translates to taste.
“Yeasts can make over 500 flavor and aroma compounds,” said Chris White, the founder of White Labs, affecting a beer’s alcohol level, clarity and texture. But while brewing yeast is one of the best-studied organisms in molecular and cell biology, exactly how its genes translate to brewing properties is still poorly understood.
By comparing the DNA of hundreds of yeasts, along with information on how they act and brew differently, “we’ll have a unique window into the genetic code,” said Prahl, who is leading the experiment. He is comparing each yeast’s sequencing information with brewing data on more than 2,000 batches of beer.
The researchers in the Belgian lab – a joint venture of the Flanders Institute for Biotechnology and the University of Leuven, Belgium – have even bigger plans.
“With this information, we’ll be able to select different properties in yeasts and breed them together to generate new ones,” Verstrepen said. “In a few years we might be drinking beers that are far different and more interesting than those that currently exist.”
“So let’s say there’s a yeast that produces an amazing fruity aroma in beer, but can’t ferment past 3 percent alcohol,” said Chris E. Baugh, a microbiologist at Sierra Nevada Brewing Co. A scientist “could then breed it with a more alcohol-tolerant strain.”
Novel yeasts are unlikely to end up in the beer of brewing giants like Budweiser, which for decades had protected its flagship lager yeast under armed guard.
“Where this is really going to take off is in the craft brewing scene,” Baugh said. The number of craft breweries and microbreweries has exploded in recent decades; they now account for 14 percent of beer sales nationwide.