Beer foam physics

The physical aspects of beer foam behavior were studied in terms of the four physical processes, mainly involved in the formation and breakdown of foam. These processes are, bubble formation, drainage, disproportionation and coalescence. In detail, the processes disproportionation and coalescence were studied. The mechanism of coalescence was determined using, amongst others, a falling film apparatus. The spreading of surface active material on the film surface proved to initiate coalescence. Disproportionation in a foam is mainly influenced by partial gas pressure differences. Surface rheological aspects dominate the rate of disproportionation when the gas composition throughout a foam is uniform. The effect of the four physical processes on various foam phenomena can be explained. The disappearance of beer foam is a result of the combined action of drainage and gas diffusion from the foam to the surrounding atmosphere. When spreading substances are added to beer foam from an external source, coalescence is initiated and foam collapse occurs. The four physical processes have a different effect on foam behavior. Therefore, a distinction between these processes was made using an optical glass-fibre probe technique. With this technique the bubble-size distribution, the gas fraction in the foam, the height of the foam and the level of the foam-liquid interface can be measured as a function of time