30 May 2012
I guess I never thought to ponder the question of why some beer bubbles rise and some sink….but good news. “Irish Mathematicians” are hard at work on the answer. This from Redorbit:
Irish mathematicians have put their minds and glasses together to understand why Guinness bubbles sink and in the end—and several beers later—they have concluded it most likely comes down to the shape of the vessel.
By running the peculiarity of this liquid dynamic behavior through a simulator, an upward flow can be seen running up from the center of the glass as a downward flow carries the bubbles down to the bottom.
The Irish mathematicians have taken these results and have shown the simulations shift when you change the shape of the glass.
Eugene Benilov, Cathal Cummins and William Lee at the University of Limerick are the mathematicians responsible for this new research, and say the shape of the glass plays a huge part in the way the beer is circulated within.
As bubbles drift upwards, they exert drag on the liquid surrounding them. The mathematicians say this drag is higher in areas where the bubble density is greatest, such as the center of the pint glass. This creates an imbalance which sets up the famous circulation pattern where the liquid flows upwards but the bubbles fall downwards near the walls.
Benilov and company say if a Guinness is poured into a straight, perfectly cylindrical pint, there would be no imbalance and the bubbles and liquid would rise together in harmony; The bubbles would constantly be replenished from the bottom of the glass.