Mystery of texture of Guinness beer: inclina…

Mystery of texture of Guinness beer: inclination angle of a pint glass is key to solution

Bubble cascade in beer is found to be analogous to roll waves observed in water sliding downhill on a rainy day

Guinness beer, a dark stout beer, is pressurized with nitrogen gas. When poured Guinness beer into a pint glass, small-diameter bubbles (only 1/10 the size of those in carbonated drinks such as soda and carbonated water) disperse throughout the entire glass and the texture motion of the bubble swarm moves downwards.

Although some models to explain how the downward movement of a bubble swarm as waves are caused in Guinness beer have been proposed, the mechanism underlying the texture-formation was an open problem.

Because the opaque and dark-colored Guinness beer obstructs the physical observation in a glass and huge computation using supercomputers is necessary to conduct numerical simulation of flows including a vast number of small bubbles in the beer, the team of researchers led by Tomoaki Watamura produced transparent “pseudo-Guinness fluid” by using light particles and tap water. They filmed the movement of liquid with a high-speed video camera applying laser-induced-fluorescence method in order to accurately measure the movement of fluid. In addition, using molecular tags, they visualized the irregular movement of the fluid.

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