We analyzed 24 beer strains from different origins by using PCR-restriction fragment length polymorphism analysis of different gene regions, and six new Saccharomyces cerevisiae x Saccharomyces kudriavzevii hybrid strains were found. This is the first time that the presence in brewing of this new type of hybrid has been demonstrated. From the comparative molecular analysis of these natural hybrids with respect to those described in wines, it can be concluded that these originated from at least two hybridization events and that some brewing hybrids share a common origin with wine hybrids. Finally, a reduction of the S. kudriavzevii fraction of the hybrid genomes was observed, but this reduction was found to vary among hybrids regardless of the source of isolation. The fact that 25% of the strains analyzed were discovered to be S. cerevisiae x S. kudriavzevii hybrids suggests that an important fraction of brewing strains classified as S. cerevisiae may correspond to hybrids, contributing to the complexity of Saccharomyces diversity in brewing environments. The present study raises new questions about the prevalence of these new hybrids in brewing as well as their contribution to the properties of the final product.