Brettanomyces are a genus of yeast found on the surface of grapes, as well as barrels, that have the ability to convert hydroxycinamic acids and vinylphenols into volatile phenols. The formation of volatile phenols has a huge affect on the bouquet of finished wine, due to the low sensory threshold of these compounds. Typical negative descriptors associated with contaminated wine are barnyard, manure, leather, tobacco, or medicinal flavours. Brett yeast proliferate in warm conditions with low sulfur dioxide levels coupled with high wine pH; thus, growth can occur at different times during the winemaking process. 4-ethylphenol is the primary compound examined due to the strong association between its presence in wine and Brettanomyces contamination. An additional sensory compound, 4-ethylguaiacol, is analyzed to estimate the impact of contamination.
Chemical analysis of target compounds is a superior choice when looking to determine contamination in wine. Other methods of detection, such as plating, are less desirable due to long incubation periods and potentially un-representative samples. Chemical quantification allows for the analysis of a uniform sample in a timely manner. GC-MS/MS is the most effective instrumentation used to isolate volatile phenols, while providing optimum sensitivity enabling these molecules to be detected at low concentrations.