Simple Test (with Alka-Seltzer) Developed to Measure Sulfur in Wine and Juice

By Amanda Garris

Graduate student Misha Kwasniewski and assistant professor Gavin Sacks developed the elemental sulfur test.

Elemental sulfur is both friend and foe in wine production: In the vineyard it is an effective method to keep the ubiquitous powdery mildew disease at bay, but excessive residues carried over into wine can result in a rotten egg aroma. Now a new, inexpensive method developed by Cornell scientists gives the wine industry a way to protect both vines and fermentations by monitoring residues and—by using Alka-Seltzer tablets.

Elemental sulfur-not to be confused with the sulfites used as a wine preservative-has been used for centuries to control fungal diseases.

 "Because it's cheap, effective, and certified for organic production, sulfur is the material of choice to control powdery mildew in the summer," said project collaborator Wayne Wilcox, professor of plant pathology based at Cornell's New York State Agricultural Experiment Station in Geneva. "Growers want to know how close to harvest they can spray sulfur-based fungicides without affecting wine quality. With no real data on how long the residues persist, there is a tendency towards extreme conservatism in sulfur use."

Differences in weather and spraying conditions make providing blanket recommendations [on when to stop sulfur sprays] difficult, so Wilcox teamed up with Gavin Sacks, an assistant professor of food science also based in Geneva who specializes in the chemistry of grape and wine aromas.  Their goal was  to develop a way to make measuring elemental sulfur sufficiently cheap, accurate, and portable that winemakers and growers can test grapes for themselves.

Food science Ph.D. candidate Misha Kwasniewski was tasked with working out a method to convert elemental sulfur into the more easily-measured hydrogen sulfide gas. The final hurdle was devising a way to remove all oxygen from the flask and flush the hydrogen sulfide into a detection tube. A research lab would use nitrogen from gas cylinders for this task, but finding a winery-friendly solution took Kwasniewski out of the lab and into the drug store.

 "I recalled a water testing kit that used Alka-Seltzer to generate carbon dioxide," Kwasniewski said. "When I tested it in our system, it actually solved three problems: it cleared the oxygen, it buffered the solution at the ideal pH for the reaction, and the carbon dioxide bubbles pushed the newly formed hydrogen sulfide gas into the detection tube."

The resulting protocol takes less than half an hour to perform, requires equipment that costs about $50, uses consumables that cost only about $5 per analysis, and could save growers thousands of dollars. (see Measuring Sulfur Residues in Juice and Wine for additional information on this test and how it has been used.)

"Elemental sulfur generally costs $10 to $20 per acre less than other powdery mildew controls," said Wilcox. "A grower with 50 acres of wine grapes who is able to use elemental sulfur in place of more expensive sprays five times during the growing season could realize savings of several thousands of dollars."

Sample sulfur detection kits have been distributed to interested growers and winemakers across New York state and extension agents in Oregon, Ohio, Virginia, and North Carolina for testing during the 2011 harvest.

The project was funded by the Canandaigua Wine Endowment Fund, Federal Formula Funds provided to state Land Grant universities in support of agricultural research, and a New York State Department of Agriculture and Markets Specialty Crop Block Grant.

Amanda Garris is a freelance writer in Geneva, New York.