Much has been written about how humans have domesticated livestock, crops and pets but what about the yeasts that we use to make bread, wine and beer? Well, scientists in Belgium examined the genomes of industrial yeast strains. These yeast strains all arose from just a few ancestors and they have undergone complex patterns of domestication.

The earliest evidence for the use of yeast to produce beer and wine comes from the early Sumerians who lived in present day Iraq. They engaged in irrigation agriculture of domesticated cereals including barley that is used in making beer. Archaeological evidence has revealed beer residue on the remains of pottery that was used for beer fermentation or storage. Using pure cultures of yeast for brewing beer, making wine or bread began in the 19th century.

However, brewers, bakers and winemakers were already using a technique called “back slopping,” which involves using a bit of a fermented product to start another fermentation. This is likely the origin of yeast domestication. Yeast strains became isolated from their natural environment, which led their evolution and adaptation to their domesticated environment. Yeast domestication is defined as the process of “human selection and breeding of wild species to obtain cultivated variants that thrive in man-made environments.”

Scientists analyzed the genomic sequences of 157 strains of yeast used for the production of wine, beer, spirits, sake and bioethanol. Not surprisingly, domesticated yeasts were genetically distinct from wild yeasts and arose from a limited set of ancestral strains. They found that domesticated yeasts fell into five groups: Asian strains used to produce sake, yeast used to make wine, yeasts used to make bread and two separate groups used in making beer. Interestingly, the beer yeasts showed more genetic adaptations as a result of domestication. The beer group was also subdivided based on geography. The beer yeasts of the U.S. split off from those in the United Kingdom in the early 1600s, which correlates with the establishment of the first brewery in America established in 1637 in the Massachusetts Bay Colony.

Beer yeasts are more diverse and have evolved to be less resistant to stress. They have a duplicate of the gene that encodes the enzyme that is required to break down the maltose sugar. The first step in brewing beer is to boil barley in water, creating a wort. The boiling water breaks down the barley and maltose accumulates. Once the wort has boiled and is cooled to room temperature, the yeast is added and begins a feeding frenzy on the maltose. When yeast eats maltose, it releases a waste product — ethanol.

Beer yeasts have evolved to live in the favorable conditions of beer fermentation and are unlikely to survive in the wild. Alternatively, wine yeast spend most of their time in and around vineyards or the guts of insects and only engage in wine fermentation for a short period of time and are closer to yeast found in the wild.

Humans have domesticated many organisms and adapted them to suit our needs including yeasts to make them better at producing many of the things we like to eat and drink.

Medical Discovery News is a weekly radio and print broadcast highlighting medical and scientific breakthroughs hosted by professor emeritus Norbert Herzog and professor David Niesel, biomedical scientists at the University of Texas Medical Branch at Galveston. Learn more at www.medicaldiscoverynews.com.

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