A Survey of Brettanomyces/Dekkera Strains for Differences in Aroma Production

Brettanomyces bruxellensis is a yeast known to cause widespread spoilage in the wine industry. However, the presence of Brettanomyces character in wine is not universally disliked or feared- some winemakers believe there are Brettanomyces strains which contribute positively to the complexity of a wine, without imparting a negative character that reduces wine saleability. In this study, 95 Brettanomyces/Dekkera isolates of global origin were screened, with the goal of determining the validity of this belief. Strains were grown in minimal media supplemented with the aromatic amino acids phenylalanine, tryptophan, and tyrosine. After a 14-day incubation period, strains were scored for intensity, likeability, and types of aromas perceived. Using these data, 16 strains were selected for growth in wine, to determine strain viability in wine, as well as aromatic compound production. Due to loss of viability in wine and no significant differences in aroma perception, an 11-strain subset was regrown in minimal media, this time including a treatment supplemented with both amino acids and the phenolic precursors to 4-EP, 4-EG, and 4-EC. Production of volatile compounds was analyzed using static headspace solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC/MS). Twenty-three compounds were tentatively identified as Brettanomyces metabolites, including 10 not previously associated with Brettanomyces. Strain effect was significant with all compounds except nerolidol. Absence of 4-EP/4-EG was correlated with poor growth. Comparisons of sensory descriptors and compound production by SPME showed no consistent correlations with the possible exception of floral aromas and phenylalanine byproducts. Fruity aroma perception did not correlate with ethyl ester production, even though these esters are known to have fruity aromas. Rotten/putrid aromas may have been related to the high fatty acid production in strain 2092, but other strains showing similar levels of fatty acids were not perceived as high in rotten/putrid character. It is suspected that masking and/or enhancing sensory effects, or sensitivity of the SPME protocol, were responsible for the lack of clearly correlated compounds and aromas. Strains 605, 2091, 2404, 2408 and 2402 are recommended for further investigation under enological conditions, to assess their viability as commercial strains.