Evaporation of a Drop of Ouzo

If you dribble a drop of ouzo  (which ouzo vendors assure us is Greece’s most popular drink) a dribbling that can easily happen if you have drunk many drops of ouzo, what happens to that drop? A newly published study peers tightly at that question:

“Evaporation-triggered microdroplet nucleation and the four life phases of an evaporating Ouzo drop,” Huanshu Tan, Christian Diddens, Pengyu Lyu, Hans Kuerten, Xuehua Zhang, and Detlef Lohse, Proceedings of the National Academy of Sciences of the United States of America, July 15, 2016. (And there’s a shorter, downloadable version.) The ouzo researchers are at University of Twente, The Netherlands, Eindhoven University of Technology, The Netherlands; Royal Melbourne Institute of Technology University, Australia; and eMax Planck Institute for Dynamics and Self-Organization, Germany. Here’s a bit of detail from the study:

“[There are] four life phases: In phase I, the spherical cap-shaped droplet remains transparent while the more volatile ethanol is evaporating, preferentially at the rim of the drop because of the singularity there. This leads to a local ethanol concentration reduction and correspondingly to oil droplet nucleation there. This is the beginning of phase II, in which oil microdroplets quickly nucleate in the whole drop, leading to its milky color that typifies the so-called “Ouzo effect.” Once all ethanol has evaporated, the drop, which now has a characteristic nonspherical cap shape, has become clear again, with a water drop sitting on an oil ring (phase III), finalizing the phase inversion. Finally, in phase IV, all water has evaporated, leaving behind a tiny spherical cap-shaped oil drop.”


The University of Twente produced a celebratory press release. A couple of videos illustrate these goings on:



BONUS: An old video of how ouzo is said to be made:

BONUS: A look back at an effect of too much whisky and candlelight. (This, too, was Dutch research.)