Ancestors of modern yeast strains domesticated in 1600

A new study conducted in Belgium has found that the wild ancestors of most modern beer and winemaking yeast strains were domesticated in around 1600.

Researchers from the Vlaams Institut voor Biotechnologie (VIB), KU Leuven and Ghent University have found that yeasts used in alcoholic fermentation, especially brewing, were domesticated by accident in the 17^th century.

The teams analysed the genomes and fermentation characteristics of 157 industrial yeasts used today in wine, beer and bread making.

As the summary of their report makes clear: “Our analyses reveal that today’s industrial yeasts can be divided into five sublineages that are genetically and phenotypically separated from wild strains and originate from only a few ancestors through complex patterns of domestication and local divergence.

“Large-scale phenotyping and genome analysis further show strong industry-specific selection for stress tolerance, sugar utilisation, and flavour production, while the sexual cycle and other phenotypes related to survival in nature show decay, particularly in beer yeasts. Together, these results shed light on the origins, evolutionary history, and phenotypic diversity of industrial yeasts and provide a resource for further selection of superior strains.”

Work on “pure” yeast strains did not take off until the 19^th century through the work of Louis Pasteur and Carlsberg brewery’s pioneering scientist, Emil Hansen, the creation of domesticated yeast cultures began, it is argued, when brewers, bakers and, to an extent, winemakers took to the practice of “backslopping”, whereby a well-fermented batch of dough or beer was kept back to be added to a new batch in order to make the next fermentation process quicker and more consistent. In the process it created isolated yeast lineages that grew and were gradually accepted or discarded as their increasingly favourable (or unfavourable) characteristics were noticed by the vintners, brewers and bakers.

Kevin Verstrepen of VIB, explained: “Without realising what they were doing exactly, these 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.”

The researchers also noted that the degree of domestication in yeast cultures was far higher in beer strains than it was in wine examples – despite both sharing the same origins.

As brewing can be done year round it is argued that yeast strains had less time to interbreed with feral yeast cultures and so became increasingly domesticated – like “dogs” according to the team.

Wine yeasts by contrast had far more time to intermingle with feral yeasts between harvests and were subsequently less predictable and controllable – like “cats”.

The full text of the study can be read here.