Why do the bubbles in stout beers such as Guinness sink instead of rising to the surface ?
It is well known that the bubbles in a glass of stout rise in the center and sink at the sides, however it has always remained a mystery why this should be so. A new study however appears to hold the answer, and the key it seems is nothing more than the shape of the glass.
"Because of the sloping wall of the pint, the bubbles are moving away from the wall, which means you're getting a much denser region next to the wall," said Dr. William Lee. "That is going to sink under its own gravity, because it's less buoyant, and that sinking fluid will pull the bubbles down. You'll see sinking bubbles not because the bubbles themselves are sinking, but because the fluid is and it's pulling them down with it."
"Irish mathematicians may have solved the mystery of why bubbles in stout beers such as Guinness sink: it may simply be down to the glass."
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Source: BBC News
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