Beer foam physics.

Ronteltap, A.D., Hollemans, M., Bisperink, C.G.J. and Prins, A.

Abstract
The main physical processes affecting beer foam properties are bubble formation, drainage, bubble coalescence and "disproportionation" (i.e. the diffusion of gas from smaller to larger bubbles, leading to an increase in the size difference between them and the eventual disappearance of the small ones). Bubbles can be formed by air trapped during dispensing, but normally arise from heterogeneous nucleation whereby carbon dioxide is liberated from solution. The other three processes all play a part in foam collapse. A fibre optic probe which measures the refractive index of the surrounding medium is described. Using this instrument to monitor the speed of foam collapse and the changes in bubble size distribution over time, the differences between carbonated and nitrogen foamed beers were investigated and the roles of the three foam collapse processes studied. It was found that disproportionation occurs in carbonated beers but not in those dispensed using nitrogen.
Keywords : beer foam stability measurement physics sensor