Whether you’re carrying your cuppa from the coffee maker to the kitchen table or toting it along for your commute, your morning pick-me-up isn’t likely to make the journey without a few small spills. Turns out, though, your bleary-eyed, non-caffeinated self may not be totally to blame. New research, published in the journal Physics of Fluids, suggests that regular liquid is more prone to spilling than that with a little foam on top. Adding a few layers of bubbles—like the layer of milk foam in a latte—seems to significantly minimize the sloshing motion of liquid.
After a team of researchers from Princeton noticed a few real-world scenarios in which foamy liquids appeared to spill less—a pint of Guinness, which is a very foamy beer, for instance, seemed less prone to spills than other pub favorites and a Starbucks latte didn’t need a lid stopper to keep it from splashing—they resolved to find out why.
The scientists first constructed a narrow rectangular container made of glass, and filled it with water, glycerol (a substance that keeps fluid thick), and dishwashing detergent to create a uniform layer of bubbles to test. The container was then subjected to two types of movement—a quick side-to-side wave and a steady rocking back and forth—and the subsequent motion was recorded with a high-speed camera. The results showed that just five layers of foam decreased the height of the fluid’s waves tenfold.
Beyond informing your coffee or beer order, researchers say the findings may help engineers develop affordable and easy ways to transport liquids, including hazardous fluids like oil and gas. In the meantime, though, don’t let the findings justify too many latte orders: a small one will set you back about 120 calories, and plain coffee has plenty of health benefits—spills aside.