Survival of Brettanomyces bruxellensis in Grape Pomace
Zachary Cartwright* and Charles Edwards
*Washington State University, School of Food Science, PO Box 646376, Pullman, WA 99164 (email@example.com)
The ability of Brettanomyces bruxellensis to survive in infected grape pomace (GP) stored under different temperatures or placed in regional vineyards was examined. B. bruxellensis strains E1, F3, or I1a were inoculated into Merlot or Syrah GP samples (~75 g) which was placed into sterile milk-dilution bottles. Samples were initially incubated at 21°C for seven days for acclimation prior to storage at 21, 10, 0, or -18°C. All strains achieved populations >105 cfu/g by day seven of storage and remained ≥103 cfu/g at 10 or 21°C for the entire testing period. In comparison, populations declined to 102 cfu/g when stored at 0°C or achieved un-detectable levels at -18°C within seven to 10 weeks. Additional GP was prepared from ongoing or completed fermentations-on-the-skins of Syrah grapes, with half sterilized by gamma irradiation (25 kGy). Samples (~100 g) were placed in steril-ized bottles capped with 0.22 µm filters, inoculated with B. bruxellensis strain I1a, and placed in two vineyards located in the Columbia Valley and one in the Walla Walla American Viticultural Areas during fall of 2014 and 2015, respectively. Bottles were periodically removed to recover viable yeast cells using a Brettanomyces enhancement medium. Overall, yeast populations increased or decreased with seasonal temperatures but remained viable (~102 CFU/g) up to 100 weeks regardless of vineyard location. Pomace samples not treated with gamma-irradiation generally had lower populations than sterilized samples and yielded a wider variation in populations corresponding to seasons: populations detected during warm months could not be recovered during cold months. As B. bruxellensis can populate GP and survive at least 100 weeks, infected winery waste dispersed into vineyards may serve as reservoirs for further dispersal during subsequent grape harvests.
Funding Support: Washington Wine Advisory Committee