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| Zuehlke |
PULLMAN, Wash. – Sulfur dioxide is one of the winemaker’s most familiar tools, helping control spoilage yeasts such as Brettanomyces and Zygosaccharomyces. When Brettanomyces, unaffectionately known as “Brett” among enologists, crosses a critical threshold, it imparts undesirable odors and flavors. Affected wines may have a spectrum of negative sensory qualities, ranging from sweaty horse to barnyard and worse.
Zygosaccharomyces, too, has a negative impact on wine quality, as it feeds on residual sugars, introducing sediment, cloudiness and, in some instances, enough gas to explode containers.
Reducing SO2 and Brett
While sulfur dioxide can prevent some of these problems, some individuals are sensitive to the chemical. Additionally, the wine industry has been striving to reduce the use of sulfur dioxide due to growing consumer interest in foods and beverages with fewer additives.
In response to this growing consumer demand, scientists at WSU and elsewhere are investigating the use of antimicrobial schemes that reduce reliance on sulfur dioxide by combining its use with other, nonchemical treatments.
Grad student explores variables
Jesse Zuehlke, a Ph.D. student in the Washington State University/University of Idaho School of Food Sciences, has pushed the science forward by investigating the interactive impact of temperature and sulfur dioxide concentration.
Zuehlke, mentored by food science professor Charles Edwards, cooled identical wine samples to four different temperatures between 10 degrees Celsius (50 degrees Fahrenheit) and 22 C (71.6 F). He introduced Brettanomyces bruxellensis and, after an acclimation period, added varying amounts of sulfur dioxide. Preliminary data showed that the combination of temperature reduction and sulfur dioxide addition had a greater effect than either treatment independently.
Zuehlke identified a sweet spot where the combo treatment had the greatest efficacy. With temperatures of 15 C (59 F) and below, a molecular sulfur dioxide concentration of 0.25 mg/L was sufficient to control the three strains of Brett that he tested in the laboratory, preventing the emergence of undesirable aromas and flavors.
This SO2 concentration is significantly below the 0.4-0.6 mg/L of sulfur dioxide often recommended for aging wine under commercial conditions.
Mango Maandazi
Beyond his lab work with wine and yeasts, Zuehlke’s accomplishments include a first-place team award at the 2012 “Developing Solutions for Developing Countries” national competition. Zuehlke served as captain of the student team that created “Mango Maandazi,” a fried bread product incorporating mangos to address harvest and nutrition issues in Kenya. For more information on the Mango Maandazi project, see http://bit.ly/KHX8h4.
As Zuehlke completes his research and anticipates graduation in May, he is looking forward to a career in food product development.
For more information on the work in Edwards lab, see http://bit.ly/Sj5bU2.