The role of grape and winery bacteria in inhibition of yeast fermentation has not been well defined. Industry samples of chronically difficult-to-ferment juices and arrested wines from the 2013 to 2015 vintages were sought from winemakers. Over 200 wines were obtained from 55 wineries, many of which displayed high bacterial levels. In 2013, one winery submitted four samples of hard-to-ferment juice and their resulting wines. All juices and 25% of the wines had bacterial contamination, including Gluconobacter, Acetobacter, and Lactobacillus species. The 2014 vintage yielded increased rates of problematic fermentations and 127 wines were submitted from 40 wineries. Twelve percent of these wines had culturable problematic bacteria, including three species of acetic acid bacteria, two Lactobacillus species, and one Pediococcus isolate. Eighty-seven wines from 18 wineries were received from the 2015 vintage, of which six to date contain acetic acid and lactic acid bacteria. In 2015, vineyard and must samples were taken on-site from three wineries that had submitted samples in previous years to determine whether the bacteria were coming from their source vineyards or were residents of the winery. Bacteria were cultured and isolated from samples and identified using 16S ribosomal DNA sequencing. Additionally, bacterial isolates were tested for their potential to induce the [GAR⁺] prion, a metabolic adaptation in yeast that can contribute to slow or stuck fermentation. Of the seven vineyards sampled, three contained at least four distinct lactic acid bacterial species. Preliminary results support the hypotheses that bacteria persist in wineries from vintage to vintage and that some organisms may be harbored on grapes in the vineyard. Bacteria previously isolated and identified from stuck fermentations have also already been shown to either inhibit yeast growth or promote the prion-induced [GAR⁺] state that reduces yeast affinity for glucose.

Funding Support: American Vineyard Foundation