How The Foam On Your Beer Keeps It From Spilling
A new study explains how your beer’s foamy top helps it from spilling, by clinging to the glass.
By Mairyn Chorney on Sep. 16, 2016

Ever wondered why you need razor sharp concentration when holding a cup of coffee or tea so it doesn’t spill over but you can walk across a crowded bar without spilling any of your beer on your hands?
Researchers from the Massachusetts Institute of Technology and École Polytechnique Fédérale de Lausanne in Switzerland wondered too and gave us an answer.
Beer Foam: Why It Stops Our Beer From Spilling
It all comes down to foam and capillary forces. Capillary action is the force that describes how droplets can form and how the surface of a liquid adheres to the side of a container.
When it comes to your beer, the foam clings to the sides of the cup and it doesn’t allow the beer to travel as far up the glass as a normal foam-free drink would. It’s the surface tension of the many tiny bubbles at the top of your beer that cling to the glass and provide a shield to movements.
The foam doesn’t have to be thick — even foam only five bubbles thick will have a measurable effect. But the thicker the foam the better at preventing spillage. Brews like Guinness would often be the least spillable beer at the bar.
Original story from American Institute of Physics.
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