Posted in Beer News, Guinness

Why Do Guinness Bubbles Sink? It’s the Glass (and Physics)

This is Big Bang Theory meets beer.  Almost literally.   If you observe a Guinness that has just been poured, you’ll notice the bubbles actually sinking down the sides, instead of rising like a regular pint.  Now – all things being equal, the gas (CO2) that leaves your beer or soda, bubbles up and out of the top because gravity is exerting more force on the the denser liquid around the bubbles.

So why  down?  Turns out the glass has everything to do with it. The bubbles get trapped on the side, and get pulled down.   Pressure forces bubbles up the center, and out.   Seems simple enough right?

Well, Irish mathematicians set out to figure out if the glass changes this phenomenon.  Bascially, they mathematically modelled the bubbles flow in a pint glass, and what they call – the “anti pint  glass.”  The bottom of the glass slopes out, or inverted from the traditional pint. [See Graphic]

If you can tell by the little arrows, the bubbles travel downward on the traditional glass, and up on the “anti” pint.  Due to higher bubble density at the edges, the central column has less drag force so the bubbles against the wall flow up.  There you have it.  Guinness bubbles explained by mathematics, and fluid dynamics.  Now go, experiment on your own. [CornellUniversity]

 The liquid density of Guinness


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