Beer
rarely spills when carrying glasses from the bar to the table, yet coffee does,
noticed Alban Sauret at Princeton University (New Scientist, 29 November 2014, www.newscientist.com).
Actually
Sauret did a study on which beverages were likely to spill the most to
determine why it was so. He mixed water with glycerol and surfactants and blew
bubbles to create stable foam on the top of the mixture. The mix allowed Sauret
and his researchers to control the size of the bubbles and the thickness of the
foam.
The
researchers rigged up a tray that would hold several beverage cups and glasses.
Then they covered several different liquids with different types of foam, and
jolted the tray – to resemble people walking from the bar in a pub to a nearby
table. Each episode was filmed to capture the sloshing motion and the videos
were analyzed. The researchers noted how the velocity of individual bubbles
related to the foam’s ability to dampen down the sloshing motion.
The
findings were that just 0.3 centimetres of foam was enough to mitigate most of
the liquid from sloshing over the side of the beverage container. With 3
centimetres of foam, the sloshing almost completely stopped.
Different
beverages produced different results. Regular coffee without foam sloshed a
lot. Café latte with foam sloshed less than regular coffee. Beer with a good
head of foam rarely sloshed out of the glass – provided it wasn’t full to the
brim. Hence researchers concluded that beer has its own anti-spill mechanism -
which is good for beer drinkers in a busy pub.
Sauret
thinks the study may have useful applications in keeping hazardous fluids from
spilling.
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