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Cloudy Beer Answer
Wed Dec 01, 2004
Listen in RealAudio 
Welcome to the final month of 2004, a year that saw the end of an 86-year old curse.
Hi, I’m Bryan Yeaton for The Weather Notebook. Today we answer our Brainstorm
about how cloud droplets are like the bubbles in beer.
JT: First, Jeff Tyler, a listener on KIOS in Omaha. I think it has to do with surface
tension, why beer and clouds are the same.
Surface tension is important, but another impetus is needed, as Rob Foster of
Indianapolis tells us.
RF: My guess is that it’s condensation because the rain droplets condense from vapor
onto small particles in the air, and I think the same process is also what forms the
bubbles in beer, and that’s why salt speeds it up, because it gives it something to
grasp onto.
Right! Although physicists call the process "nucleation." From Bossier City, La., Allen
Smith fills in some details.
AS: In both cases the bubbles ( in the case of beer and the droplets in the case of
clouds) form around impurities, or tiny particles, such as a dust particle in the air or
impurity in the beer. So, if both the beer and the atmosphere were completely free of
impurities, they wouldn’t have anything to form around, and we wouldn’t have the
bubbles and particles.
The nucleation sites for beer bubbles are actually microscopic cracks in the wall of the
bottle.
Paul Niesen, who listens on Alabama Public Radio, has done his homework:
PN: I've noted, through two decades of extensive research, that the better beers which
demonstrate the most active carbon dioxide coalescence seem to be the German Pils.
Likewise, a good, mid-summer Kansas thunderstorm seems to do the trick for water
droplets.
If you like this Brainstorm, pick up Craig Bohren’s book, Clouds in a Glass of Beer, in
your holiday shopping. The Weather Notebook is supported by Subaru of America.
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