Bubbles percolating up through a freshly poured glass of champagne do more than just tickle the tongue, according to a new study.
A team of European researchers, publishing in this week's Proceedings of the National Academy of Sciences, finds that the bubbles in sparkling wine drag compounds that activate smell receptors to the surface of the sparkling wine and then shoot them upward where a taster can easily encounter them. (Although "champagne" technically refers to sparkling wines from the Champagne region of France, all effervescent wines should be subject to the same mechanism.)
Using mass spectrometry, the researchers parsed the chemical makeup of the wine itself and that of the tiny droplets in the headspace, or the area above the liquid's surface. Those droplets, or aerosols, are sprayed upward in a fountain of tiny jets as bubbles of dissolved carbon dioxide rise to the surface of the champagne and then burst. A typical 0.75-liter bottle of champagne, the study's authors estimate, contains roughly five liters of CO2 gas, enough to form tens of millions of bubbles.
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"We have demonstrated that the chemistry of those champagne aerosols is quite different than the chemistry of the liquid bulk itself," says lead study author Gérard Liger-Belair, a professor in the laboratory of enology (wine studies) and applied chemistry at the University of Reims Champagne–Ardenne in France. Specifically, the aerosols are loaded with so-called surface-active compounds—chemicals that are attracted to interfaces between gas and liquid—some of which play a role in conveying the aroma of the wine. (Even when a substance is on the tongue, aromatics contribute to flavor, which is a blend of taste and smell.)
Surface-active molecules, Liger-Belair explains, are drawn to the gas–liquid interface of the champagne bubbles, which are simply pockets of CO2 gas surrounded by liquid, and are then pulled upward to the surface of the beverage when the bubble rises. "A bubble is a perfect trap to get these surface-active molecules," he says. "Bubbles act like a lift."
When the bubbles burst, the concentrated surface-active compounds are thrown several centimeters into the headspace, where they can meet a taster's nostrils. "They are projected into the form of these aerosols, which are overconcentrated with surface-active molecules, some of them showing aromatic properties," Liger-Belair says.
Susan Ebeler, an analytical chemist and enologist at the University of California, Davis, says that even in still wines, the chemical signatures between the liquid in the glass and the vapor in the headspace differ. But "the bubbles add a very interesting dimension" to the partitioning of chemicals in wine, she adds. "What they're actually seeing here is that the carbonation is forming aerosols that can carry these compounds into the headspace. So this is a more complex sort of release."