Characterization of ethyl phenols and other volatile components in Brettanomyces bruxellensis off-flavor occurrence
Brettanomyces bruxellensis contributes flavors to wine which are described as Band-aid,
burnt plastic, smoky, spicy, leathery, horse sweat, and barnyard. While winemakers
debate whether the ‘Brett’ aroma should always be considered an off-flavor, there is a
consensus reflected in the AVF funding priorities that an improved understanding of
Brettanomyces will assist the winemaking community. Building on previous work
performed at Cornell, we had proposed several microbiological and chemical studies for
the 2007-08 research cycles. Specifically, our objectives were to investigate B.
bruxellensis volatile phenol production in relation to the precursor concentration and to
the yeast growth phase. Five strains of B. bruxellensis strain were studied in model wine
with variable levels of hydroxycinnamic acid (HCA) precursors. For all strains, we
observed similar growth kinetics for concentrations up to 5 mg/L of the HCA precursors.
At 10 mg/L of HCA precursors, yeast growth was slowed during the exponential phase,
but the final yeast concentration was unchanged. Volatile phenol production was highly
correlated to HCA level for all initial precursor concentrations. The conversion
efficiency of HCA precursors (1-10 mg/L) to volatile phenols was greater than 50% in
most cases, with the exception of 4-EP production by B. bruxellensis strain 2091 (<30%).
4-EP production was more differentiated among strains and started slightly later than 4-
EG. In summary, this work has demonstrated that early detection of most strains of B.
bruxellensis before the midpoint of the exponential growth phase can allow for
intervention prior to production of volatile phenols, that at least one strain is capable of
producing detectable levels of phenols much earlier in growth, and that potential volatile
phenol production is well predicted by precursor concentration.