Identification of Vineyard and Winery Bacteria and Their Impact on Problematic Fermentations

Book excerpt: In 2013 one winery requested assistance in identifying inhibitory microbes from their wines that had high populations of acetic and lactic acid bacteria. This work continued that analysis of inhibitory bacteria from wines. In response to an open request Californian winemakers submitted samples of problematic juices and arrested or sluggish wines in 2014 and 2015. Juices and wines were plated on a general enriching medium, 1/2 MRS agar, to identify viable bacterial species present in the samples. 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 sent in from 40 wineries. 12% of these wineshad culturable problematic bacteria including three species of acetic acid bacteria, two Lactobacillus species, and one Pediococcus isolate. 87 wines from 18 wineries were received from the 2015 vintage, of which four contained culturable acetic and lactic acid bacteria. Additionally, in 2015, vineyard and must samples were taken on-site from three wineries that had submitted samples in previous years to determine if 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, bacteria 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, four contained five distinct lactic acid bacteria species. Fermentations sampled showed a higher incidence of acetic acid bacteria that appeared within the first three days of fermentation along with a lower incidence of lactic acid bacteria. Results support the hypotheses that problematic bacteria are persisting in wineries from vintage to vintage and that some organisms are harbored on grapes in the vineyard. The bacteria isolated and identified from stuck fermentations, vineyards, and musts have also been shown to either inhibit yeast growth or promote the prion-induced [GAR+] state that reduces yeast affinity for glucose.