There's rarely time to write about every cool science-y story that comes our way. So this year, we're running a special Twelve Days of Christmas series of posts, highlighting one story that fell through the cracks each day, from December 25 through January 5. Today: the physics of champagne bubbles.
It's New Year's Eve, and revelers around the globe will be breaking out the bubbly in massive quantities to usher in 2019. Why do humans love champagne and other fizzy beverages so much, when most animals turn up their noses when it's offered? Roberto Zenit, a physicist at Mexico's National Autonomous University of Mexico, and Javier Rodriguez-Rodriguez of the Carlos III University of Madrid in Spain, posit in the November issue of Physics Today that carbonation triggers the same pain receptors in our deep brains that are activated when we eat spicy food.
"This bubbly sensation you have when you drink a carbonated beverage basically triggers similar taste buds," said Zenit. "Champagne is just wine; what makes it special is the carbonation. It's a sad day when you drink flat champagne."
He and Rodriguez-Rodriguez study the behavior of various fluids (including paints), and carbonation is a particularly fascinating topic within that discipline. When the bubbles in champagne burst, they produce droplets that release aromatic compounds believed to enhance the flavor further. (When bubbles in a carbonated beverage like beer don't burst, the result is a nice thick head of foam.) And here's another interesting fact: the bubbles in champagne "ring" at specific resonant frequencies, depending on their size. So it's possible to "hear" the size distribution of bubbles as they rise to the surface in a glass of champagne.
It's better with bubbles
Most modern fizzy drinks owe a debt to 18th-century British chemist Joseph Priestley. Carbonization as a natural process was known at the time, in the form of underground springs subjected to high pressures that easily absorbed carbon dioxide, making the water "effervescent." But Priestley invented an artificial carbonation process while living next to a brewery in Leeds. Ever the scientist, he started experimenting with the CO2 used by the brewery and found that a bowl of water placed above a fermenting liquor became slightly acidic to the taste, just like natural mineral waters. He included his simple instructions for artificial carbonation in a 1772 treatise, Impregnating Water with Fixed Air.
Champagne actually predates Priestley by at least 150 years: the first mention of a sparkling wine dates back to 1535 in the Languedoc region of France. The classic brand Dom Perignon gets its name from a 17th-century monk who had the job of getting rid of the bubbles that developed in his abbey's bottled wine, lest the pressure build up so much they exploded. Legend has it that upon sipping such a bubbly wine, the monk realized the bubbles might not be such a bad thing after all, declaring, "Come quickly, brothers, I am drinking stars!"
Champagne is usually made from grapes picked early in the season, when there is less sugar in the fruit and higher levels of acid. The grapes are pressed and sealed in containers to ferment, just like any other wine. CO2 is produced during fermentation, but it's allowed to escape, because what you want at this stage is a base wine. Then there is a second fermentation, except this time, the CO2 is trapped in the bottle, dissolving into the wine. Striking just the right balance is key. You need about six atmospheres of pressure and 18 grams of sugar, with just 0.3 grams of yeast. Otherwise the resulting champagne will either be too flat, or too much pressure will cause the bottle to explode.
Gerard Liger-Belair, a physicist at the French National Center for Scientific Research (CNRS) at the University of Reims in northeastern France, has been studying the physics of champagne for years and is the author of Uncorked: The Science of Champagne. He doesn't imbibe his experimental samples—usually by the time he's done, the fizz is all gone anyway. But he has gleaned numerous insights into the underlying physics over the years by subjecting champagne to laser tomography, infrared imaging, high-speed video imaging, and mathematical modeling.
For instance, the size of the bubbles plays a critical role in a really good glass of champagne. Larger bubbles enhance the release of aerosols into the air above the glass—bubbles on the order of 1.7mm across at the surface. "This result undermines the popular belief that the smaller the bubbles, the better the champagne," Liger-Belair told the Telegraph in 2016. "Small bubbles were the worst in terms of aroma release."
Tips for the tipsy
Here are a few more pro tips to bear in mind as you imbibe this evening. Definitely drink your champagne chilled to about 39°F. This reduces how much alcohol gets carried up in each bubble (too much alcohol can overpower the champagne's more delicate flavors). It also will keep the cork from being expelled too forcefully when it's popped. Tilt the glass when pouring to avoid a bubbly overflow.
And it really is true that champagne is best drunk from a flute, rather than the wider "coupe" glass supposedly modeled on the breast of the 18th-century French queen Marie Antoinette. Apparently the fluted shape produces more aroma-rich CO2 just under the imbiber's nose, the better to enhance the flavor. However, Liger-Belair actually recommends using a tulip shaped wine glass, to cut down on CO2's natural acidity.
There is one class of people who definitely should not be breaking out the bubbly this New Year's Eve: astronauts aboard the International Space Station. According to Zenit and Rodriguez-Rodriguez, in such low gravity, the bubbles in champagne don't bubble to the surface; they just stay right where they were formed. Granted, food scientists managed to modify Coca-Cola and Pepsi in 1985 for testing aboard the space shuttle Challenger, and the space shuttle Discovery boasted a soda dispenser in 1995.
But there would be serious digestive issues should an astronaut actually drink it on board, since in microgravity the bubbles grow to enormous sizes, resulting in a frothy beverage with a substantially larger gas-to-volume ratio than the earthbound counterpart. "Unable to escape the liquid in the digestive system, the gas would produce painful bloating of the astronauts' stomach and intestines," the authors write. "For relief, one could only burp, but in the microgravity environment, the burp was often wet, much like the experience of acid reflux."
Check. No champagne or soda in space.
DOI: Physics Today, 2018. 10.1063/PT.3.4069 (About DOIs).