Humans have a long relationship with the yeasts that make beer. Genetic and phenotypic analysis of 157 strains of Saccharomyces cerevisiae yeast used by the fermentation industry now reveal that they all originate from a few common ancestors and evolved in ways to make brewers happy. The work, led by Kevin J Verstrepen and Steve Maere of the Flemish Institute for Biotechnology in Belgium, also found that beer yeast possesses, in contrast to wild yeast, duplicated genes that help to break down maltotriose, a sugar in beer mash. Many also evolved a mutation that prevents production of 4-vinylguaiacol, which is known to taint the flavour of beer. Beer yeast has also lost its ability to reproduce sexually, which would be needed to survive in a wild environment. On the other hand, wine yeast can still reproduce sexually, presumably because wine-making only happens in the autumn and the yeasts therefore have to get by without human support during the rest of the year.