Did you just hear that record scratch? Me too. Generally, an overly foamy head is bad news for beer drinkers—this isn’t a college kegger, after all. But scientifically, there’s a great reason to appreciate that inch or so of bubbles: Turns out, they keep more of your beer in your glass.
Fluid dynamics researches at the French National Center for Scientific Research in conjunction with colleagues from Princeton University and the École Normale Superieure de Cachan found that a beverage’s foam acts as a sort of barrier that slows down tiny waves in your glass. The researchers conclude that the foam lightly clings to the sides of the glass, preventing spillage (in science terms: “The motion of the foam along the walls of the container damps sloshing through viscous dissipation.”) Using a contraption that created waves and bubbles, hooked up to a high-speed camera, scientists concluded that foam shortened the amplitude of a liquid’s waves by as much as 90 percent.
Scientists say this research also holds true for other foamy beverages, meaning a latte is less likely to slosh over the sides of your mug than coffee is. Of course, if you’ve spent all night knocking back 11% imperial stouts, all the foam in the world won’t get that next beer from bar to table safely.