How Medieval Brewers Made Beer Taste Good

September 8, 2016 | Erica Tennenhouse

beer brewer
Photo credit: Public Domain (image has been cropped)

Genetic study reveals the history of beer yeast domestication.

These days, beer brewers have a plethora of yeast strains at their disposal — one imparts a crisp apple flavor, another gives off the distinct taste of clove, and so on.

New research published in the journal Cell reveals that the wild ancestors of modern beer and winemaking yeast strains were first domesticated by medieval brewers in the late 1600s — that’s recent history, considering beer brewing dates back roughly 6,000 years.

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Scientists built a timeline of yeast domestication by sequencing the genomes of more than 150 different strains of baker’s yeast currently used to make beer, wine, sake, bread, and bioethanol. They conclude in their paper that “the thousands of industrial yeasts that are available today seem to stem from only a few ancestral strains that made their way into food fermentations and subsequently evolved into separate lineages, each used for specific industrial applications.”

The initial selective pressures on baker’s yeast were most likely unintentional. As study senior author Kevin Verstrepen of Belgium’s Flanders Institute for Biotechnology explains in a press release, “Ancient brewers, winemakers and bakers often practiced 'backslopping', a technique where a small part of a previous well-fermented dough or brew was kept apart to mix it with a new batch, to make the fermentation process quicker and more consistent.”

“Without realizing what they were doing exactly, these ancient craftsmen were effectively selecting and transferring yeast cultures from one batch to the next, allowing the microbes to continuously grow and adapt to man-made industrial environments," he continued.

Many of the changes that the yeast strains have undergone are written in their DNA. For example, the researchers found that the genes involved in fermenting sugar to alcohol have been duplicated, which has sped up the brewing process. Also, certain genes that produce undesirable flavors carry mutations — these mutant yeasts would have been selected by early brewers because the beers they produced tasted better.

Interestingly, the genetic signatures of domestication were stronger in the yeast strains used for beer than those used for wine. “This is probably because wine yeasts are only used to ferment grape juice once a year, and survive in and around the winery for the rest of the year, where they may interbreed with feral yeasts,” says study lead author Brigida Gallone of Ghent University in Belgium.

The scientists intend to use their yeast genome library to produce superior strains, with the hopes of ultimately creating tastier wines and beers.

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