Survival of Brettanomyces bruxellensis in grape pomace and reduction of populations by application of heat and sulfites

Abstract

Background and Aims: Spreading grape pomace in vineyards could promote dispersal of the spoilage yeast, Brettanomyces bruxellensis. Thus, we evaluated the ability of this yeast to survive in inoculated pomace stored at variable temperature as well as in regional vineyards. Methods and Results: Three strains of B. bruxellensis were inoculated into Syrah or Merlot pomace which was stored at 21, 10, 0, or –18°C. All strains maintained ≥104 colony-forming units (CFU)/mL at 21 or 10°C for 10 weeks but declined to ≤103 CFU/mL when incubated at 0 or –18°C. Additional Syrah pomace, half sterilised by gamma irradiation, was inoculated with B. bruxellensis, placed into sterilised bottles capped with 0.22 μm filters, and placed into three vineyards. Overall, the yeast population increased or decreased with varying seasonal temperature but remained viable (~103 CFU/mL) for up to 130 weeks regardless of vineyard location. Non-sterilised pomace generally had a population lower than that of sterilised samples and yielded wide variations in population corresponding to seasons. The recovery of Brettanomyces from infected pomace was reduced, if not prevented, by heating to ≥50°C and adding 45 mg/L total SO2. Conclusions: As B. bruxellensis can survive at least 130 weeks in pomace, infected winery waste dispersed in vineyards may serve as a reservoir for the continued contamination of grape harvests. Such contamination can be minimised by heating potentially infected pomace to ≥50°C for at least 10 min and adding sulfites is recommended. Significance of the Study: Long-term survival of B. bruxellensis in pomace was established and microbial control strategies using heat and sulfites demonstrated.