The popular beverage Guinness—a dark, creamy Irish stout—has long fascinated physicists due to its unusual fluid dynamics. Now, a team of Japanese researchers have attempted to unravel the mysteries of how the drink behaves in a study published in the journal Scientific Reports.
Anyone who's ever enjoyed the famous beverage will know that after it is poured into a pint glass, many of the bubbles can be seen to move downward. This is counterintuitive because bubbles in a liquid tend to rise to the top because of the difference in density.
Some previous research has attempted to explain why the bubbles move downward—with one paper suggesting it could be down to the shape of the glass. However, studying the fluid dynamics of Guinness is difficult because its dark color makes it hard to conduct physical observations in a glass.
To get around this problem, the team led by Tomoaki Watamura from Osaka University created a transparent "pseudo-Guinness fluid" using light particles and tap water. They then performed experiments on the bubble distribution in Guinness when it was poured into three different types container—a pint glass, an inclined rectangular container and a trapezium-shaped container—to observe how the texture forms.
They filmed this setup using a high-speed video camera and applied a special laser observation technique to accurately measure the movement of the fluid.
They found that when the drink is poured, small bubbles about a tenth of the size of those found in Budweiser or Champagne disperse throughout the entire glass, helping to create its unique creamy texture.
While this helps to explain why the bubbles in Guinness descend in the glass, it is not the only factor at play, according to the researchers.
"The investigation has concluded that when Guinness is poured into a typical pint glass, which widens towards its top, the rising motion of bubbles creates a clear-fluid (bubble-free) film above the inclined wall," the authors wrote in the study. "The dense clear-fluid film falls, whereas the bubble-rich bulk rises, which is known as the Boycott effect."
According to Watamura, the results of the study have implications for the study of several physical systems.
"There are a large number of small objects in nature, such as fine rock particles transported from rivers to the sea and microorganisms living in lakes and ponds," he said in a statement.
"Comprehending and regulating the movement of small objects is important in various industrial processes as well. Our research results will be useful in understanding and controlling flows of bubbles and particles used in industrial processes as well as protein crystallization and cell cultivation used in the field of life science."
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Aristos is a Newsweek science reporter with the London, U.K., bureau. He reports on science and health topics, including; animal, ... Read more
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