Why do beautiful cascading bubble patterns form when you pour Guinness into a glass? An assistant professor at Japan’s Osaka University and fan of the iconic stout devoted himself to emptying as many as 200 cans — solely for experimental purposes — to get to the bottom of this mystery.

A group led by fluid dynamics scholar Tomoaki Watamura, 33, took on the challenge of solving the workings behind the sinking bubbles in a glass of stout — a unique fluid motion unseen in other carbonated drinks whose bubbles usually rise from the bottom of the glass. After testing 400 ways of filling glasses under various conditions, while emptying as many as 200 cans of Guinness alone in the process, the team reached the following conclusion: The beautiful bubbles result from a superb combination of the stout beer’s tiny bubbles and specific glass conditions.

Guinness beers contain nitrogen gas, and their bubbles have a diameter around one-tenth of regular carbonated drinks’.

To investigate the bubbles’ formation mechanism, Watamura performed simulations using hollow glass beads to represent the bubbles, and filled containers resembling beer glasses with tap water, while observing the beads’ movement. When the container’s inside surface was positioned upward at a right angle, the sinking bubble patterns did not form. But when the simulation was tested out repeatedly while slanting the container’s inner walls, it was found that the bubble pattern formed at a slight 10- to 20-degree angle.

Upon observing the details of the part where the wave pattern of bubbles emerged, Watamura found that on the inner surface, the container’s contents were divided into a layer with many bubbles and another consisting only of liquid, which was caused by slanting the container.

Furthermore, he witnessed the liquid-only layer slide toward the bottom of the container along its slanted inner surface. The researcher formed the theory that a wavelike pattern is created as this layer of liquid sinks through the bubbles at fixed intervals. A similar pattern is also seen in rainwater flowing down the surface of car glass — a phenomenon called “roll wave” in fluid dynamics studies.

To find out why the cascading bubble flows are not present in other carbonated drinks, the team conducted simulations using a supercomputer. After running some 400 simulations in which the container as well as the size and amount of bubbles was altered, it was discovered that the wave pattern did not form in other beverages because the bubble particles drift apart and lead to a lower density.

The researchers finally concluded that an exquisite combination of the minuteness and density of the bubbles with the sloped inner surface of the container played a significant role in the patterns’ emergence. There was no relation between the sinking bubbles and how the beer is poured.

The findings have been shared in publications including a British journal specializing in physics, and apparently it could be useful for developing water purification technology where impure substances attach to bubbles’ surfaces.

Watamura became a Guinness fan in his student days, after being attracted to the creamy bubbles that distinguish it from other beer, and even visited a factory abroad. In 2008, he encountered a paper with a hypothesis on the bubble pattern formation, and began pursuing it as a research topic in 2016 after his appointment as an assistant professor at Osaka University.

He has emptied around 200 cans of Guinness for his experiments. Despite observing stout bubbles in various containers, he smiled and said, “Still, I like the pattern made when you pour it in a Guinness glass the most.” His next endeavor is to “be able to control the patterns created.”

Research team member Mihoko Suzuki, from Kirin Holdings Co.’s Institute for Future Beverages, said, “The value of beverages is in their appearance, and Guinness epitomizes this. The world of physics, which might seem a distant realm, unfolds in the beer glass we’re all familiar with. I’d like people to enjoy drinking it while keeping these points in mind.”

(Japanese original by Koki Matsumoto, Osaka Science & Environment News Department)

Source Mainichi Japan

By Arsalan Ahmad

Arsalan Ahmad is a Research Engineer working on 2-D Materials, graduated from the Institute of Advanced Materials, Bahaudin Zakariya University Multan, Pakistan. LinkedIn: https://www.linkedin.com/in/arsalanahmad-materialsresearchengr/