Look closely at a glass of champagne, and you’ll notice that the bubbles stream upwards in organised single-file chains.
But in a glass of carbonated water, the bubbles zoom up from many different directions, veering about as they do.
A group of US and French fluid mechanists have figured out why champagne forms these stable “bubble chains” when other bubbly drinks don’t.
Read more: Bubbles! The physics of champagne
Their findings, published in Physical Review Fluids, could also be used to explain bubble flows in industrial processes.
“This is the type of research that I’ve been working out for years,” says senior author Professor Roberto Zenit, an engineer at Brown University, US. “Most people have never seen an ocean seep or an aeration tank but most of them have had a soda, a beer or a glass of champagne. By talking about champagne and beer, our master plan is to make people understand that fluid mechanics is important in their daily lives.”
The researchers investigated the bubbles in different fizzy beverages, including carbonated water, beer, champagne and some other sparkling wines. Champagne and sparkling wine have stable bubble chains, while the chains are only sometimes stable in beer and usually unstable in mineral water, making for much more random-looking bubbling.
The team filled a rectangular plexiglass container with each drink, then added a needle to the bottom to pump in gas and make their own, controlled bubbles in the drink.
They then either increased the bubble size of the gas bubbles they were pumping in, or added “surfactants” – substances that soften the border between two different fluids, like air and water. Surfactants are used as foaming agents in soaps and other bubbly products, and surfactant proteins appear naturally in champagne and beer.
“The theory is that in champagne these contaminants that act as surfactants are the good stuff,” says Zenit.
“These protein molecules that give flavour and uniqueness to the liquid are what makes the bubble chains they produce stable.”
The researchers found that adding surfactants could produce stable bubble chains in the unstable drinks.
Confirming and explaining their results further with computer modelling, they believe that the surfactants in champagne let the bubbles leave smooth wakes, so the next bubble can rise easily in exactly the same path.
This explains why carbonated water, with no surfactants, tends to have unstable bubble chains.
“This wake, this velocity disturbance, causes the bubbles to be knocked out,” says Zenit.
“Instead of having one line, the bubbles end up going up in more of a cone.”
The researchers also found that blowing bigger bubbles could smooth much of this out, allowing for stable bubble chains without extra surfactants.
Aside from some nice pub trivia, the team say these results will be useful for other fluid mechanics problems.
For instance, they’ll be relevant to examining carbon dioxide and methane vents on the ocean floor, and operating aeration tanks at water treatment plants.
“We’re interested in how these bubbles move and their relationship to industrial applications and in nature,” says Zenit.