Friday, June 2, 2023

Solved at last: the mystery of why champagne bubbles go straight up

From the pop of its cork to its delicate golden hue, champagne has many features that make it a celebratory tipple – but none are as recognisable as its fine fizz.

Now researchers have shed new light on the quintessential sparkle, revealing why champagne bubbles rise in a straight line, unlike those of many other drinks.

“Our intuition, from studying bubble dynamics, is that bubbles rising in line do not follow a straight line. The wake behind each bubble knocks out the trailing bubble behind to the side,” said Prof Roberto Zeni, the co-author of the study from Brown University, Rhode Island, in the US.

But, he added, this is not the case for champagne and some types of beer.

According to Zeni, the unusual trait is down to particular ingredients in champagne that not only give it flavour but attach to the bubbles, changing the motion of the fluid immediately behind them as they rise and hence allowing the bubbles to form a chain.

“These molecules, which attach to the bubble surface, induce changes in the wake which, in turn, cause the bubbles to not be knocked out from the in-line configuration,” said Zeni.

Writing in the journal Physical Review Fluids, Zeni and colleagues in the US and France describe how they came to their conclusions by conducting a series of experiments in which nitrogen bubbles were introduced to a tank filled with a mixture of water and glycerin.

“These are mock analogs of champagne,” said Zeni. The team varied both the size of the bubbles and the levels of detergent like chemicals in the mixture, known as surfactants.

The results revealed that as the size of the bubble increased, the bubbles began to form stable chains, meaning the bubbles rose through the fluid in a straight line. A similar effect was seen when the bubble size was kept constant and the concentration of surfactant was increased.

The team carried out calculations to explore these effects, noting that whether bubbles form a straight line depends on the twisting motion, or vorticity, created in the fluid behind a rising bubble.

While increasing bubble size can affect the vorticity, allowing stable bubble chains to form, the fine bubbles of champagne suggest a different mechanism is at play.

The authors say that the straight lines of tiny bubbles within champagne are down to flavour molecules, such as fatty acids, within the drink that have surfactant properties.

When these molecules attach to the surface of a bubble, they change its surface tension, making the bubble more deformable when it comes to forces acting at right angles to its motion but more rigid, and “non-slip” with respect to forces acting at a tangent.

“[Together these effects] create more vorticity, which in turn contributes to changing the nature of the wake which determines if bubbles can remain in line,” said Zeni.

But it seems the research is not only helpful in explaining curiosity of champagne.

“Understanding why bubbles rise in line or dispersed has important implications for other problems, like industrial processes or natural phenomena,” he said.

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