Scientists Explain Why Regular Coffee Spills, but Latte's Don't

Have you ever wondered why foamy latte is less likely to spill than a cup of coffee? Turns out, it's all because of the foam.

Emilie Dressaire, an assistant professor of mechanical and aerospace engineering at the New York University Polytechnic School of Engineering, first thought about foam as a damping mechanism was when she was handed a latte at Starbucks and told she probably would not need a stopper to keep it from spilling.

While studying the physical dynamics of sloshing liquids, researchers found that five layers of foam bubbles limited the height of waves ten-fold as compared to plain liquid (like black coffee).

"What we observe in our cups of coffee, this happens every time you're carrying liquids in a container that's partially filled," study co-author Emilie Dressaire, an assistant professor of mechanical and aerospace engineering at New York University, told Popular Science.

"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," Alban Sauret, a researcher at the French National Center for Scientific Research (CNRS), said in a press release.

Their full findings are published in the journal Physics of Fluids.