INTERACTIONS BETWEEN ETHANOL, STORAGE TEMPERATURE, AND SULFUR
DIOXIDE THAT AFFECT BRETTANOMYCES BRUXELLENSIS IN MERLOT WINE
Abstract
By Taylor A. Oswald, M.S.
Washington State University
May 2017
Chair: Charles G. Edwards
Brettanomyces continues to be a spoilage problem in red wines. Compositional and
environmental conditions that favor growth remain undefined. Using a commercially-prepared
Merlot wine, a 5 × 4 factorial experimental design was employed with ethanol (12%, 13%, 14%,
15%, or 16% v/v) and temperature (12°, 15°, 18°, or 21°C) as variables. Culturabilities of two
strains of B. bruxellensis isolated from Washington wines (I1a and F3) were monitored for 100
days before concentrations of volatile acidity (VA), 4-ethylphenol (4-EP), and 4-ethylguaiacol
(4-EG) were measured. While growth was observed in 12% to 15% ethanol, lag phase duration
generally increased with a decrease in temperature. Culturabilities quickly declined in wines
containing 16% v/v ethanol, with rapid losses at 21°C. The two strains demonstrated similar
growth patterns, except in wines containing 15% ethanol where F3 showed reduced growth at
higher temperatures (18° and 21°C) compared to I1a. Wines in which Brettanomyces reached
>106 cfu/mL had concentrations of 4-EP and 4-EG above sensory thresholds (440 µg/L and 47
µg/L, respectively). In a separate experiment, a 2 × 2 × 3 factorial design was employed with
ethanol (13% or 14.5% v/v), temperature (15° or 18°C), and total SO2 (0, 60, or 100 mg/L) as
iv
variables. The addition of 100 mg/L total SO2 to wine resulted in inhibition of Brettanomyces
growth in wine containing 14.5% v/v ethanol. It is therefore recommended that risk of spoilage
associated with B. bruxellensis can be reduced through higher concentrations of ethanol, storage
temperatures ≤12°C, or the addition of 100 mg/L total SO2 in wines containing ≥14.5% v/v
ethanol.
v