Bacterial community dynamics during distilled spirit fermentation: influence of mash recipes and fermentation processes.

Production of ethanol from sugars and yeast is an ancient, ostensibly simple process. The source of sugars varies depending on the desired product and can include fruits, vegetables, molasses, honey, or grains, among other things. The source of yeast can be natural in the case of spontaneous ferments, but dry yeast addition is typical for large-scale fermentations. While the polymicrobial nature of some alcoholic fermentations is appreciated (e.g., for wine), most grain-based ethanol producers view microbes, apart from the added yeast, as "contaminants" meant to be controlled in order to maximize efficiency of ethanol production per unit of sugar. Nonetheless, despite rigorous cleaning-in-place measures and cooking the mash, bacteria are routinely cultured from these fermentations. We now know that bacteria can contribute to fermentation efficiency on an industrial scale, yet nothing is known about the makeup and stability of microbial communities in distilled spirit fermentations. The work here establishes the roles of mash recipes and distillery practices in microbial community assembly and dynamics over the course of fermentation. This represents an important first step in appreciating the myriad roles of bacteria in the production of distilled spirits.