Between Thanksgiving and New Year’s, sales of sparkling wines spike, as humans celebrate the holidays — especially the New Year — with champagne toasts. Since it’s about time to pop open that bottle of bubbly, here are a few things you should know:
The bubbles are basically yeast farts
We have yeast to thank for alcohol, and we should thank it twice for alcohol with bubbles. These microscopic fungi extract energy from sugar using a process called fermentation, and produce alcohol and carbon dioxide as waste.
To generate enough carbon dioxide to make bubbles, winemakers actually need to ferment champagne twice. That’s because the grapes in champagne aren’t very sweet, so there isn’t a lot of sugar for the yeast to eat. After the first round of fermentation, the wine is only about nine percent alcohol, which is pretty low — your average glass of champagne is usually closer to 12 percent. And the carbon dioxide is allowed to escape, so no bubbles form.
In the second round of fermentation, winemakers add a little bit of extra sugar — either cane or beet — and, more yeast. Then, they cap the bottle, sealing everything inside. The yeast ferment the sugars and produce more carbon dioxide and alcohol. They also die, and digest themselves, producing the molecules responsible for the more toasty, yeasty flavors in aged champagne.
There are a couple of ways to remove the yeast when the wine is ready. In the traditional method used for champagne, the winemaker turns the bottles on their heads to collect the yeast near the bottle’s mouth, and dips the neck of the bottle in an ice bath — creating a plug of frozen yeast and sediment. Then, the winemaker opens the bottles, and the pressure that’s been building inside during fermentation pushes out the frozen yeast plug. The winemaker replaces the lost volume with wine, sugar, or a mix — and corks the bottle. For other sparkling wines, this second fermentation step sometimes occurs in a big tank rather than in the bottles themselves.
There’s more pressure inside champagne bottles than inside tires
Because the bottles are sealed during fermentation, the carbon dioxide molecules can’t escape as a gas, so they dissolve in the wine. Sealed inside the bottle, this creates a massive amount of pressure — about three times the air pressure inside your car’s tires, according to the chemistry website Compound Interest.
If the carbon dioxide were allowed to expand as a gas, it could probably fill six bottles of champagne, according to a 2012 review paper by champagne expert Gérard Liger-Belair. Liger-Belair is a professor on the ‘effervescence team’ at the Université de Reims Champagne-Ardenne in France. He called champagne bubbles a fantastic playground for fluid physicists in an email to The Verge. “It is simply amazing to discover such a subtle science hidden right under your nose each time you enjoy a glass of [bubbly],” he said.
Uncorking the bottle and pouring the wine into a glass upsets the delicate balance that kept the carbon dioxide dissolved in the champagne. There’s a chemistry law that basically says the concentration of a gas dissolved in a liquid is proportional to the pressure of that gas in the atmosphere above the liquid, according to Chemical & Engineering News. When the cork is on the bottle, there’s a ton of carbon dioxide trapped in the little headspace between the wine and the cork — so a lot of carbon dioxide stays dissolved in the liquid. When you take that cork off, the headspace becomes the entire room where there’s a much lower concentration of carbon dioxide. So the carbon dioxide rushes out of the wine to try and restore that balance. That’s where the bubbles come in.
There are about 1 million bubbles in a champagne flute
When you pour a glass of champagne, about 80 percent of the carbon dioxide escapes invisibly through the liquid’s surface through a process called diffusion. The rest forms the bubbles so characteristic of bubbly.
The bubbles are actually born inside the champagne flute — forming on little imperfections and impurities that let the carbon dioxide molecules collect together to make a bubble. When scientists filmed champagne using high speed video and a microscope, they realized that most bubbles start on pieces of lint that had probably floated into the glass as dust, or were left behind by a towel.
That’s why we shouldn’t thoroughly clean our champagne flutes — and shouldn’t let them near the dishwasher, says Ronald Jackson, a wine expert, former botany professor, and author of Wine Science: Principles and Applications. For optimal bubbling, he recommends wiping out the glasses with a dry rag before using them.
When a bubble becomes too buoyant, it detaches from the little piece of lint where it was born, and floats up to the surface — leaving room for another bubble to start forming in its place. That’s why you get those nice lines of bubbles rising to the surface in a champagne flute, growing in size as they collect more carbon dioxide during their ascent.
There’s some controversy over exactly how many bubbles leave your champagne flute, but according to Liger-Belair’s calculations, the best estimate is around 1 million if you pour straight down the middle.
Use a flute, not a coupe for extra bubbliness
Some wine aficionados enjoy drinking flat champagne (“It’s interesting, but it’s flat,” Jackson says.) But most people buy it for the bubbles. And the best way to preserve those bubbles is to chill the wine, which slows down the gas molecules, pour at an angle, and use a champagne flute.
In fact, while champagne may form about 1 million bubbles if you just dump the bubbly into your glass, you could probably get tens of thousands more to effervesce if you pour more gently down the side of the glass to better preserve the carbon dioxide, Liger-Belair adds.
He also used an infrared carbon dioxide imaging technique to watch how much carbon dioxide floats off the champagne’s surface, and he discovered that much less leaks invisibly through the surface of a small-mouthed champagne flute. It practically gushes out of champagne in a wider mouthed coupe glass, because there’s much more champagne exposed to the air. The more carbon dioxide that’s lost to diffusion means less carbon dioxide left to make bubbles.
And, for the love of champagne, don’t make one of those Gatsby-esque champagne towers. You’ll lose the vast majority of bubbles, Jackson says. “It may be good for show, but not for appreciation from the point of view of the wine.” Oh, also, don’t wait too long to drink it — because the cork doesn’t perfectly seal the bottle. The longer champagne ages in the bottle, the lower the bubble count.
The jury’s out on whether it makes you drunker
Champagne hangovers are notorious — but the jury’s out on exactly why. There have been two very small studies studies that compared the blood alcohol content of people drinking bubbly versus flat champagne, and carbonated versus still cocktails.
“It is simply amazing to discover such a subtle science hidden right under your nose each time.”
When people drank the carbonated drinks, they did get an earlier spike in their blood alcohol concentrations than when drinking the still drinks. In the champagne study, people drinking bubbly showed an early spike in alcohol levels after about five minutes. When they drank the flat champagne, it took about 15 minutes to be similarly drunk, but after that the effects of the drink were about the same. So, the bubbly hit the participants harder, faster. But in the end they didn’t get any drunker from a single glass.
Damaris J. Rohsenow, who studies alcohol but did not participate in this research, thought it was a well designed study. “The cross-over design controlling for simply the carbon dioxide is excellent and shows that the bubbles themselves do affect intoxication,” she said in an email to The Verge. Still, it’s small, there was a ton of individual variation in the results, and it’s far from conclusive.
In the cocktail study, 14 out of 21 participants absorbed the alcohol in the carbonated drink faster than from the still drink. The rest either didn’t show a change or absorbed the carbonated booze more slowly. A couple of mechanisms have been floated, including that the carbonation helps the booze move faster out of the stomach and into the small intestine, where most of the alcohol is absorbed. Another possible explanation is that the bubbles shoot alcohol into the airspace above the drink, where it’s inhaled. But, we really don’t know — and given the scientific funding climate, we might not find out for awhile.
As for why champagne hangovers are so brain-poundingly miserable? There’s a pretty straightforward answer: you probably drank too much of it.
“I don’t know any science behind it,” says Richard Olsen, a neuroscientist who studies the effect of alcohol on the brain. “I can only say that people have said that, and a lot of those are people who don’t usually drink as much as they did that time they had the champagne for some birthday, or New Year’s, or whatever — and so that’s why they had the hangover.”
Unfortunately, we can’t blame tomorrow’s champagne hangovers on anyone but ourselves.