Redox Control of Chardonnay Fermentation to Limit Conversion of Elemental Sulfur to Hydrogen Sulfide
Sami Young,* Caroline Merrell, Torey Arvik, and
Roger Boulton
*Jackson Family Wines, 27000 Ramal Rd, Sonoma, CA,
95476
(samantha.young@jfwmail.com)
Elemental sulfur (So) is commonly used in vineyard management to
control powdery mildew. However, the presence of So residues
during fermentation can lead to unwanted reductive aromas,
primarily through formation of hydrogen sulfide (H2S). Oxidation
reduction potential (ORP), or redox potential, is an effective
tool to measure the chemical state of fermentations. When the
redox potential of a wine drops below 100 mV (standard hydrogen
electrode scale), the spontaneous chemical reduction of So to H2S
can occur. The goal of this project was to determine if redox
control during fermentation could prevent chemical reduction of
So to H2S.
Chardonnay juice with 25 mg/L So added was fermented in
triplicate with and without redox control. The setpoint for redox
control was 150 mV (standard hydrogen electrode scale) and was
achieved through the addition of air. The redox potential was
monitored continuously in all six fermentations and total soluble
solids and H2S were measured every 24 hrs. In each replicate, 9 L
of juice was fermented in 5-gallon buckets using RC212 yeast, at
an average fermentation temperature of 22°C. On average,
redox-controlled replicates completed fermentation two days
earlier than uncontrolled replicates. H2S production peaked
between days 2 and 3 of fermentation and reached 21 ± 32 ppb in
the redox-controlled fermentations and 222 ± 19 ppb in
uncontrolled fermentations. At the end of fermentation, H2S
levels were 2 ± 2 ppb in the redox-controlled group and 99 ± 73
ppb in the uncontrolled group. During fermentation, the
redox-controlled group produced twice as much total free
sulfhydryls (including glutathione) than the uncontrolled group.
The results of this study demonstrate that the controlled use of
air to control redox potential during wine fermentation can not
only significantly reduce the formation of H2S when So is
present, but can also lead to shorter fermentation times.
Funding Support: Jackson Family Wines
