![width="400px"](https://igor.wdfiles.com/local--resized-images/sparks:vanilla-and-milk/width="400px"/medium.jpg)
Description: When I've made recipes in which I pour a teaspoon (5 ml) or so of vanilla into a bowl of cold milk, it causes peculiarly exuberant flows. I pour it in from a height of a few centimeters, the vanilla appears to spread over the surface. Then for several seconds (up to 20s) the milk pulses up to the surface with rapid flows.
I would guess that by pouring in the vanilla, some of it gets incompletely mixed with the milk. These lower density parcels of fluid then rise to the surface at irregular intervals. Possibly the vigor of the flows may have something to do with their having a higher alcohol content, and therefore lower surface tension, which may cause the surface to spring away a bit, dragging more fluid upwards and outwards. However, this explanation does not seem to satisfactorily explain the long delays, or quite match the flows.
The attached video shows the response, though not as strongly as some times.
Page creator's name: Mickey von Dassow
Page creator's contact info: Through IGoR contact link.
cooking flow fluid-flow physics surface-tension
Created: 29 Mar 2014 19:05
Updated: 06 Jan 2015 21:42
Comments: 05 Apr 2014 21:07
#Comments: 1
From the FYFD tumblr the terms for these types of phenomena are solutal convection and the Marangoni effect (flows driven by differences in surface tension), though the vanilla+milk results in somewhat different (and far less dramatic) flows than the examples shown.
Btw, the milk used was homogenized whole milk, which may have some effect on density and surface tension.