Brewer’s yeast is a relatively new in the history of beer. In 1857 Louis Pasteur discovered yeast’s role in fermentation, paving the way for today’s refined use of modern brewer’s yeast strains. Before this, brewers introduced fermentation with the addition of sediment from a previous batch or alternatively allowed fermentation to begin spontaneously by exposing the un-fermented beer to air. Unsurprisingly, many beer styles produced in this way involved fermentation with what we now consider spoilage organisms. In this talk we will discuss beer fermentation by organisms other than brewer’s yeast, along with beer styles that rely on fermentation by these organisms.