You might say that a master brewer is to yeast what a dog breeder is to a champion purebred. Both disciplines harness the power of artificial selection, also known as selective breeding. As Harvard microbiologist and avid homebrewer Sarah Douglass explains, “when you add yeast to sugar, you’re putting them into into their ideal environment for rapid evolution via rapid growth. You might see several generations of yeast live, reproduce, and die in a single fermentation.”
To keep things consistent, commercial brewers “spike” each fermentation with an initial batch of yeast. Large batches of these flagship yeast are kept deep frozen in suspended animation. Yet eventually even these stocks run out, at which point scientists do their best to recreate the lost flavor profile using other strains of yeast.
What about creating yeast strains in the lab? “We do have the technology to make all sorts of molecular changes in yeast,” Douglass told me. “But flavor is such a complex trait, with so many metabolic pathways involved, that we’re much better off using artificial selection to find yeast strains that make tasty beer. Trying to engineer a tasty yeast strain from scratch, by deleting genes or turning up protein expression, would be very difficult.”