Email Print Share

"Foamation" -- The Discovery Files

The Discovery Files
Audio Play Audio
The Discovery Files podcast is available through iTunes or you can add the RSS feed to your podcast receiver. You can also access the series via AudioNow® by calling 641-552-8180 on any telephone.

Princeton researchers have revealed how the tiered structure of a cafe latte develops when espresso is poured into hot milk. Flowing liquids into each other to yield desired layers could reduce costs and complexity in a range of applications, such as industrial flows and mixing procedures in "process technology."

Credit: NSF/Karson Productions

Audio Transcript:
'Foaming' a conclusion.

I'm Bob Karson with the Discovery Files, from the National Science Foundation.

Ever wonder about the café latte you just ordered? How it evolves (latte foaming sound) from that chaotic first pouring and mixing of fluids...into organized, distinct layers?

Me neither. But somebody has. One day a professor at Princeton was intrigued by an unsolicited email with an image of a café latte. It soon became the inspiration for a study of the physics of... layered fluids.

The team started making lattes in the lab, but to more precisely control the layering, they came up with a new recipe: dyed water in place of the hot coffee and dense, salty water in place of the milk. (...that'll wake you up in the morning). Using a camera, LEDs and tracer particles, the team was able to see the movement of fluids and create mathematical models.

The primary finding: a phenomenon known as "double-diffusive convection"... a heat exchange within a given denser, cooler liquids sink, while lighter, hotter liquids rise. When the density within an area evens out, the fluids have to flow horizontally instead of vertically, creating the bands or layers. They also found velocity was a factor...pour too slowly and the liquids just mix.

The beauty of fluid mechanics in a coffee cup could lead to advances in mixing procedures with applications from industry to medicine and beyond.

(coffee counter) ...yeah, I’d like a half-caf double diffusive convection with just a touch of nutmeg...

General Restrictions:
Images and other media in the National Science Foundation Multimedia Gallery are available for use in print and electronic material by NSF employees, members of the media, university staff, teachers and the general public. All media in the gallery are intended for personal, educational and nonprofit/non-commercial use only.

Images credited to the National Science Foundation, a federal agency, are in the public domain. The images were created by employees of the United States Government as part of their official duties or prepared by contractors as "works for hire" for NSF. You may freely use NSF-credited images and, at your discretion, credit NSF with a "Courtesy: National Science Foundation" notation. Additional information about general usage can be found in Conditions.

MP3 icon
NSF podcasts are in mp3 format for easy download to desktop and laptops, as well as mobile devices capable of playing them.