There’s a reason Champagne bubbles rise in neat straight lines

Have you ever gazed into your Champagne flute at a party and been mesmerized by the endless, uniform march of bubbles rising up from the base of the glass?

If so, you share that experience with an international group of researchers, who decided to investigate why bubbles in carbonated drinks behave the way that they do.

They were inspired to pursue this question not only for the sake of good old-fashioned curiosity, but also because there are a wide range of practical reasons to study bubble chains, said Roberto Zenit, a professor of engineering at Brown University who co-authored the study.

“This research is important to answer questions about natural phenomena and industrial applications where bubble motion is important,” said Zenit, whose research group has long studied bubble dynamics, in this case, “how a volume of gas moves inside a liquid” within a two-phase bubbly flow.

Two-phase flows play a role in a variety of processes, from the production of penicillin to ocean seeps, or methane bubbles that emerge from the ocean floor, Zenit explained. Unraveling the mystery of bubble dynamics, he said, is key to understanding these systems.

“So basically, it’s just an excuse to explain bubbly flows in everyday life,” he said.

To crack the code, Zenit and his colleagues observed bubbles within several liquids, including sparkling water, beer and Champagne, and used numerical simulations to calculate quantitative measurement of forces within them, like the velocity of the bubbles and the fluid around them.

READ MORE: The food science behind what makes leftovers tasty (or not)

Their big conclusion? One way small bubbles can remain in a stable chain like you see in a Champagne flute is if the liquid they’re moving through contains molecules that attach to their surface, making the bubbles more rigid.

“Apart from a new way to appreciate a glass of champagne, these findings bring us one step closer to understanding the complicated physics behind bubbly liquids,” Carmen Lee, a postdoctoral researcher in physics at North Carolina State University who was not involved in the study, told the PBS NewsHour via email. She added that bubbly liquids have “a wide range of applications.”

But what does all of this actually mean? Answering that question requires a brief crash course in physics. Here’s how Champagne bubbles pull off their neat, elegant dance, and why the findings of this research are important for other industries.

Getting bubbly with physics

Carbonated drinks like Champagne are examples of a two-phase flow. The term “phase” in this case refers to states of matter; the two phases in Champagne are the liquid itself and the dissolved carbon dioxide gas responsible for the bubbles.

There are a few things key to understanding this flow. One is deformation, or the effect of application of a force to a material. If you put a rubber band around your fingers and stretch it out, that’s an example of deformation. A force applied to a liquid, on the other hand, results in flow, or continuous deformation.

“That non-stopping deformation is what we call flow, and that’s what liquids do,” Zenit said. “To bring water to your house, you apply this force using a pump and that causes the flow.”

When bubbles travel through liquid, they can experience deformation. Small bubbles often keep their spherical shape, while large bubbles are more prone to this phenomenon. That’s because pressure develops around objects as they move through liquid, and that pressure becomes a force when it’s applied across their surface, Zenit explained.

READ MORE: The smoky science behind what makes food grilled over an open flame taste so good

Pressure is what’s responsible for deforming bubbles, he added, but whether it’s successful depends on the surface tension of the bubble in question. If the surface tension force is greater than the pressure force — as is seen with smaller bubbles — it won’t deform. But if the pressure is greater than the surface tension, bubbles can deform, Zenit said.

Another important factor: Vorticity, a measure of the rotation of the fluid particles, or the swirl that trails an object as it moves through a liquid.

“A bubble, when it’s rising in a liquid, has as a wake — has a trail of motion behind it …” Zenit said. “So basically the fluid inside the wake is rotating.”

The wake of one bubble determines what happens to the one that comes after it. Which brings us to the question of how bubbles do or don’t remain in a stable chain. In Champagne, the key to bubbles’ behavior lies in surfactants, or flavor molecules that occur naturally in the liquid.

When these flavor molecules bind to the surface of the small bubbles in Champagne, those surfaces become rigid in a process called surface immobilization. When that happens, the amount of deformation the bubbles cause as they move through the Champagne increases, creating a larger amount of vorticity in their wake.

This induces a negative lift force that keeps each bubble in line with the one above it. Without surfactants, the small bubbles in Champagne wouldn’t have enough vorticity to create the negative lift force that paves the way for the neat bubble chains.

Animation by Megan McGrew/PBS NewsHour

In liquids like beer, bubbles create a smaller amount of vorticity and generate a positive lift force, which means that any bubble approaching another one above it will get knocked out of the way, creating a kind of cone shape. In this case, the lift force becomes destabilizing as opposed to stabilizing, Zenit said.

The bubbles in beer are sometimes stable, he added, but other times they’re not. More research would be necessary to understand which molecules are responsible for influencing them one way or the other.

“For the case of Champagne, small bubbles remain stable because of surfactants, and for other cases, large bubbles without surfactants would also be stable,” Zenit said. “So there’s two ways to gain stability. One is through size, through deformation, and the other one is through the surface immobilization because of surfactants.”

The conclusions Zenit and his colleagues made in their research aren’t necessarily new, Jesse Capecelatro, an associate professor in the departments of mechanical and aerospace engineering at the University of Michigan who was not involved in this research, told the PBS NewsHour via email. But the authors of the study “seem to provide quantitative evidence for the first time,” he said.

Capecelatro also noted that glass shape — which wasn’t addressed in the study — could also influence circulation patterns in the flow that would in turn affect bubble stability.

What else can bubble dynamics tell us about the world?

Exploring whether bubbles remain stable or not are examples of the same physics that determine what goes on at the bottom of the ocean or inside an oil well.

Bubble column reactors are “at the heart of many multiple industrial processes,” Capecelatro noted, including algae production and waste management. In these reactors, he explained, bubbles often move in a “heterogeneous regime” defined by random patterns and large clumps that influence how they mix with the liquids around them and, in turn, how well they work.

“The tendency for bubbles to cluster or move in chaotic patterns is difficult to predict and design around, and insights like this can help engineers design optimal reactors,” Capecelatro said.

Different types of bubble behavior have various uses, whether they’re unstable and dispersed within a liquid or moving in a stable, single-file line. Unstable bubbles cause a lot of agitation in a liquid compared to stable chains, Zenit said.

Better understanding of both phenomena — plus being able to predict whether bubbles will be stable or unstable based on a certain set of conditions — can allow engineers to plan accordingly and harness their various industrial applications.

“The ability to predict what will happen is what this fundamental understanding of physics gives you,” Zenit said.

So next time you sit down with a carbonated drink, take a moment to appreciate the tiny lab in your glass.