Impact of Brettanomyces Yeast on Wine Flavor: Sensory Description of Wines with Different

Growth of the yeast Brettanomyces/Dekkera in wine can drastically alter the aroma characteristics to the point where all varietal and regional flavor characteristics are overwhelmed by the flavors produced by these yeasts. To avoid spoilage it is important to know more about the aromas formed by these yeasts and be able to detect the changes in aroma early so that further growth of the yeast and further aroma modification can be avoided. Two groups of commercial wines with suspected "Brett" character were evaluated by two trained panels of judges. The first group included four Cabernet Sauvignon and two Pinot Noir wines; the second included four Cabernet Sauvignon wines. All were evaluated by sensory descriptive analysis and GC/MS 4-ethyl phenol analysis. Characteristic "Brett" aromas such as plastic, burnt plastic, Band-aid (TM), cow manure, barnyard, and horse sweat were summarized by the first group of tasters as 'plastic.' For the second group 'plastic' included only pastic, burnt plastic, and Band-aid (TM) odors. Dry manure and sweaty/animal were separate descriptors. In both groups, the wines were differentiated by univariate analysis of variance (ANOVA) and multivariate discriminant analysis (DA) by two descriptors: plastic and fruity. The greatest fruit character and lowest plastic scores defined the younger Cabernets, and the opposite was true for the older wines. There was little difference between the two Pinot Noirs for either descriptor. The a priori "Brett" observations from the winemakers proved to be a consistent predictor of Brett character for all wines. The observations also agreed with the 4-ethyl phenol concentrations and the post-hoc plastic mean scores from the ANOVA analyses. The "strong Brett" wines were the older vintage wines with higher 4-ethyl phenol concentrations, higher plastic and lower fruity mean scores. Wines with "maybe some" and "no Brett" had the lower 4-ethyl phenol concentrations and more fruit with less plastic scores. This investigation shows that aroma modifications by Brettanomyces yeasts can be reliably detected and quantified with trained tasters. Further investigations into the chemical basis of the 'Brett' aromas will allow us to use chemical indicators to detect activity of these yeasts early