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Dear Dr. Vinny,
Why don’t we see the perlage in a closed bottle of sparkling wine? And why do we only see them when the bottle is opened? What happens?
—Simone, Belem, Brazil
You’re correct that perlage (an elegant word for “string of bubbles”) isn’t visible in a sparkling wine (or in a bottle of soda, for that matter) while the bottle is sealed. At that point, carbon dioxide—the gas that causes the bubbles—is dissolved into the liquid and kept trapped by the pressure inside the closed bottle. Keep in mind that the pressure in there is somewhere from 70 to 90 pounds per square inch, or up to two or three times the amount of air pressure in the tires on a car.
When you open a bottle of any carbonated beverage, you hear the sound of escaping carbon dioxide—that delightful pop or whooshing sound. And given the pressure of the carbon dioxide trapped in the bottle, and how relatively little air pressure there is outside the bottle, suddenly the carbon dioxide isn’t kept dissolved in the liquid anymore, hence the bubbles that form as it’s trying to escape.
The amount of carbon dioxide that can remain dissolved into a liquid is also proportional to how cold the liquid is. Warm bubbly, beer or soda is much more fizzy as the carbon dioxide escapes rapidly. The colder the liquid, the slower the stream of bubbles, and the slower the carbon dioxide is being released.
Bubbles also don’t really form in the middle of a liquid—say, in the middle of a sea of Champagne. (How I wish I were in the middle of a sea of Champagne right now!) Bubbles form at what are called “nucleation sites,” which are tiny defects or irregularities in the surface of the Champagne glass or other container, where the gas can collect into a bubble.
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