Development of an enrichment medium to detect Dekkera/Brettanomyces bruxellensis, a spoilage wine yeast, on the surface of grape berries.

Brettanomyces bruxellensis spoilage is a serious problem for the wine industry. Mainly, by producing 4-ethylphenol and 4-ethylguaiacol, it confers off-odors to the wine and changes its aromatic quality. The presence of B. bruxellensis cells on the berry was speculated but it had never been clearly demonstrated. On grape berries, the microbial ecosystem is highly diverse and the population of B. bruxellensis can be very small. The aim of our study was to reveal and confirm the presence of B. bruxellensis on the surface of grape berries. We developed an enrichment medium for B. bruxellensis in order to overcome the detection limit of the molecular methods (species-specific PCR, ITS-RFLP PCR, PCR-DGGE). This medium, named EBB medium, made it possible to detect B. bruxellensis after 10 days of culture. For the first time, the presence of B. bruxellensis has been clearly established in several vineyards and at different stages of the grape development after the veraison. This work led to the conclusion that the grape berry is the primary source of B. bruxellensis. Grape growers and winemakers should take these results into account when deciding on the treatment to apply in the vineyards and the must. With the information provided here, B. bruxellensis prevention could start in the vineyard.