When it comes to keeping their wine safe from oxidation—the chemical reactions with air that can spoil a wine—the tools at a winemaker’s disposal are limited. After fermentation, vintners try to limit oxygen exposure, and they choose bottle closures with care. Many also add sulfur dioxide, which is effective in ensuring chemical stability, among other things, but which in excess can mask some of a wine’s aromas.
Researchers have begun to ask, however, whether there might be another measure to prevent oxidation. Taking a cue from food manufacturers, Prof. Andrew Waterhouse and his team at the University of California at Davis began to look at the chemical compounds found in wine—mostly transition metals iron and copper—that serve as oxidation catalysts. By binding these metals with ions known as chelators, Waterhouse reasoned, they could prevent this catalyzation. A paper recently published in the Journal of Agricultural and Food Chemistry confirms this hypothesis.
“We found that we could really control the extent of oxidation, at least in a model wine system, with these chelators,” Prof. Ryan Elias, of the Department of Food Sciences at Pennsylvania State University and a coauthor of the paper, told Wine Spectator.
For their study, the researchers created a model wine—a solution mimicking wine made of ethanol, tartaric acid and a phenolic. They observed the effects of four different chelators on this solution, focusing on the ions’ ability to bind to iron. Iron atoms cycle between two different states, gaining and losing electrons. This cycle, known as reduction-oxidation, or “redox,” is what catalyzes oxidation. It creates free radicals, which react with organic compounds in wine to undesirable ends. For example, radicals can help form acetaldehyde, the antecedent of vinegar’s main component, acetic acid; they can also lead to the loss of thiols that contribute to a wine’s sensory characteristics.
“Our approach was to control that [redox cycle],” said Elias, “by either binding up those metals, or binding them in a certain state so that they can’t go back and forth.”
The four chelators observed for this study produced different effects. The key, Elias emphasized, is that these ions can help us learn to control oxidation, whether that means preventing even the slightest oxidative note from entering into a fresh, early-drinking Sauvignon Blanc or encouraging some oxidation in a long-lived Cabernet Sauvignon that will take up a vintner’s precious cellar space for years before being bottled.
The true upside of chelators, however, may lie in their potential to reduce the amount of sulfur dioxide needed in winemaking. Elias doubts that the need for SO2 will ever be completely eliminated. “It’s so profoundly effective,” he said, especially in its ability to prevent other problems with microbes. But in conjunction with the antioxidative measures already in the winemaker’s arsenal, he suggested, “chelators could be another technique that you could use to prolong the fragile [aroma] compounds that are really oxidizable.”
The scientific community is still years away from making any recommendations to winemakers. Elias noted that many concerns remain to be addressed, including the behavior of chelators on real wine and the selection of appropriate chelators. Some chelators imbue their own aromas and tastes on a wine, and some are toxic; the goal, Elias said, is to discover ones that are effective, naturally occurring and food-grade.
“What we’ve shown is academic,” he admitted, “but it informs our next step.” After all, Elias said, “the more tools that we can give winemakers to control oxidation, the better.”