Why a long black spills more easily than a latte

Coffee inspires many a workplace but it had a direct affect on research into the wave-damping effects of foams in liquids, as the Washington Post reports.

Emilie Dressaire, who’s now an assistant professor at NYU Polytechnic School of Engineering, started thinking about the integrity of foamy liquids when a Starbucks employee told her she wouldn’t need a lid stopper to keep her latte from spilling. Her colleague Alban Sauret, now a researcher at the French National Center for Scientific Research, had recognized the same difference in foamy beers.

His colleague was more of a beer man.

“While I was studying for my Ph.D. in the south of France, we were in a pub, and we noticed that when we were carrying a pint of Guinness, which is a very foamy beer, the sloshing almost didn’t happen at all,” said Alban Sauret, who is currently a researcher at the French National Center for Scientific Research (CNRS).

The experiences led them to a study, just published in the journal Physics of Fluids.

A glass container was filled with water, soap, and glycerol and created uniform layers of tiny bubbles into the liquid.

By rocking the containers back and forth using different motions, they were able to record the behavior of the liquids as they became foamier and foamier. They recorded the tiny waves produced by the shaking with a high-speed camera. Sure enough, their foam made the liquid more stable. Five layers of bubbles lowered the wave height by 10 times compared with plain liquid.

The findings have more implications than just stopping you spilling your coffee, though.

“Our findings suggest that foam could be used in various industrial processes in which sloshing needs to be minimized” particularly in the transportation of dangerous liquids, such as hazardous waste or oil, the report says.

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