The owner of Air’s Champagne Parlor in lower Manhattan, Ariel Arce, pours a sampling of Ulysse Collin’s terroir-focused single-vineyard Champagnes: a Blanc de Noirs and a Blanc de Blancs. The Blanc de Noirs sparkles vigorously on the palate—“joyously,” says Arce—with bright pinpricks of effervescence accentuating the tangy, assertive red fruit. The Blanc de Blancs is richer, suave, and dense, and its much gentler fizz of ultrafine bubbles suits it. In this sample, she says, the effervescence is “a pleasure texture.”
The sparkle of a sparkling wine isn’t an added-on frill but an essential part of its character, and the way the bubbles behave exerts a surprisingly strong influence on the way in which the person drinking it experiences the wine. The basic physics are simple. In the same way that sugar dissolves more easily in hot tea than in cold water, carbon dioxide gas dissolves more easily in a colder liquid than in a hotter one.
The Influence of Carbon Dioxide
Inside a bottle of sparkling wine, there are no bubbles. The wine is bottled at high pressure—90 pounds per square inch is common for Champagne, for example—and at that pressure, the liquid is able to hold a lot of dissolved carbon dioxide. When the bottle is opened and the wine poured, the liquid suddenly finds itself at normal atmospheric pressure, at which point physics dictates that much less carbon dioxide is able to stay dissolved in the liquid. It has to escape, which it does primarily in the form of bubbles. The more carbon dioxide that’s dissolved in the liquid during winemaking, the greater the pressure in the bottle, and the bigger and more assertive the bubbles are when it’s poured.
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The other crucial factor in the behavior of bubbles is temperature. Because carbon dioxide dissolves more readily the colder a liquid is, a wine served a few degrees warmer will fizz significantly more—and lose its fizz sooner—than if it’s served colder.
Much of this bubble behavior has been extensively studied and documented by Gérard Liger-Belair, a professor of chemical physics at the University of Reims Champagne-Ardenne and the author of Uncorked: The Science of Champagne. Liger-Belair has devoted his career to the detailed study of Champagne and its effervescence; he’s published studies with such titles as “Ascending-Bubble-Driven Flow Patterns Within Glasses and Their Impact on Gaseous CO2 and Ethanol Release Under Standard Tasting Conditions.”
The most important factor in the experience of sparkling wine’s sparkle, Liger-Belair says, is the amount of gas in the wine to start with. The more dissolved carbon dioxide, the more fizzy a wine will be when poured—and the larger the bubbles will be. “The level of dissolved CO2 has a direct influence on the bubble size,” he says, “because bubbles grow through diffusion of CO2 from the liquid phase to the gas phase into the bubble.”
Over years in a cellar, carbon dioxide slowly leaves a bottle through its porous cork. That’s why an aged Champagne has a finer fizz than a freshly disgorged one: There’s simply less carbon dioxide in it, which means the bubbles are fewer and smaller.
“Temperature does not much affect bubble size,” Liger-Belair points out, but he says it does affect viscosity. At slightly warmer temperatures, a wine is less viscous, thinner—“and therefore the [greater] the velocity of bubbles,” he says. “Generally, Champagne drinkers much prefer bubbles rising slowly [as it’s] more visually appealing, and therefore a cold wine is preferable. But if the wine is too cold, aromas are less perceived by the drinker.” There’s no perfect serving temperature, he adds, suggesting it’s a matter of compromise.
In one fascinating experiment, Liger-Belair scoured wineglasses with powerful acid to remove any dust particles or fibers, then filled them with Champagne. “In such a perfectly clean glass,” he found, no bubbles appeared. It “looked like a still wine,” he says. The dissolved carbon dioxide made its escape as usual—but imperceptibly, rising off the surface of the wine without fizz.
That’s because for a bubble to form, it needs a birthplace, a microscopic pocket of air to help it emerge from the liquid. Most commonly, such nucleation sites are invisible hollow cellulose fibers shed from a cleaning cloth onto the inner surface of the glass. Wherever there’s a fiber, a tiny gas bubble forms in the liquid and then rises through the wine, growing in size as it picks up more carbon dioxide, until it bursts on the surface.
How Bubbles Contribute to Flavor and Aromas
Bubbles in wine aren’t just for show. Their bite is enjoyably perceptible in the mouth, a phenomenon that used to be attributed to the physical bursting of the bubbles but is now understood to be a biochemical effect. When you take a sip of a sparkling beverage, a little carbon dioxide diffuses into the cells of your tongue, where it activates particular nerve endings, producing a sharp tingle. The tactile sensation makes up much of the pleasure of the mouthfeel of any sparkling beverage, whether it’s the eye-opening burn of ice-cold seltzer, or the fizzy caress of a vintage Champagne.
There is a syndrome called Champagne blues that occurs when mountain climbers on a regimen of anti-altitude-sickness drugs crack a bottle at a summit and find themselves with a celebratory mouthful of flat-tasting, acrid bubbly. The altitude drug Diamox inhibits the tongue enzyme involved in the tingle and therefore makes Champagne (or any carbonated drink) taste terrible.
In addition to their sensory tingle—and a mild tart taste associated with dissolved carbon dioxide—bubbles also powerfully potentiate other flavors. As they form at the bottom of a glass and rise to the surface, they create currents in the wine that help circulate the liquid in the glass; then, when they rise to the surface and burst, they launch tiny aromatic plumes of wine mist into the air above the glass. This contributes to the sensory impact of sparkling wine at least as much as the taste of the carbonation does. Even some perlants—wines that aren’t obviously sparkling, like many Vinhos Verdes—contain enough dissolved carbon dioxide to boost their aromatic impact when they’re poured.
The traditional slender flute glass maximizes the distance traveled by a rising bubble, and hence the amount it grows, and released carbon dioxide collects in the flute’s constricted volume of space above the wine—which, Liger-Belair says, “could promote the very unpleasant carbonic bite in your nose when you smell above the glass. Serving Champagne and sparkling wines in a traditional still-wine glass is better—it prevents carbonic bite and helps you better appreciate aromas.”
Andrew Rastello, the assistant wine director at Eleven Madison Park, recently decided to stop serving Champagne in traditional flutes and use fuller-bowled wineglasses instead. “Being able to stick your nose in the glass and smell it,” says Rastello, “is like somebody turned the lights on. As I start to see that change in other restaurants around the city, I’m glad. It makes a drastic difference.”
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Paul Adams is the senior science research editor at Cook’s Illustrated. He lives in New York City, where he writes about food and drinks.