Understanding Beer Foam with Dynamic Fluid-Film Interferometry

Foams are commonly found in industrial processes like froth floatation, wastewater treatment, and scrubbers. They are also an important part of consumer products like bread or the foam on a glass of beer. The characteristics of the foam such as the density, mechanical properties, and stability, are dependent on the properties of the surface-active compounds that are present in the liquid.

In the present work, dynamic fluid-film interferometry is utilized to study the time evolution of films captured between a single bubble and the (initially) planar air/solution interface. This technique can be used to track the topological features of the film as a function of time, from which the dynamics of drainage can be quantified. Some of the metrics presented here include the radial extent of the film, the total volume of the film, and the maximum, minimum, and mean film thicknesses. These data are then compared to the dynamic evolution of complete foams formed by sparging air bubbles into a small volume of liquid. Results will be presented for simple surfactant solutions, as well as a range of beers, with the goal of enabling the prediction and/or control of foam characteristics by tuning the properties of the air/solution interface.