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

The popularity and production of whiskey have grown dramatically in recent years. During whiskey fermentation, lactic acid bacteria (LAB) are a major concern since they can outcompete yeast and spoil the fermentation. However, some bacteria present in the fermentation could potentially counter this effect and promote fermentation efficiency. To better understand the possible roles bacteria play in yeast-based whiskey fermentations, we examined bacterial community dynamics across fermentation stages and investigated how variation in the mash recipe affects bacterial community composition and fermentation efficiency. To this end, we collected 193 samples from three distilleries at the beginning (Cook/set), middle (Fermentation), and end (Drop) of whiskey fermentation, with six mash recipes sampled from one distillery. We used high-performance liquid chromatography (HPLC) to quantify the contents of sugars, organic acids, and ethanol, which revealed distinct differences between distilleries and mash recipes. High-throughput Illumina Miseq sequencing of the 16S rRNA gene V4 region revealed that bacterial communities shifted toward Firmicutes during the fermentative conversion of sugar to ethanol, especially Lactobacillales. Mash recipes also influenced sugar composition, fermentation efficiency, and microbial dynamics. Recipe-specific operational taxonomic unit (OTU) biomarkers in Drop samples included Leuconostoc for corn, Lactococcus for wheat, and Lactobacillaceae_unclassified for rye, while Escherichia/Shigella was associated with sorghum, suggesting potential suppression of LAB.