Studies on the physical and compositional changes in collapsing beer foam

Batches of foam were characterised by analysis of conductivity and quantitative changes in mass and solute composition of material retained both within foam and foam drainage. The conductivity of dispensed beer foam declined exponentially during the initial stages of foam collapse, followed by a secondary or consolidation stage characterised by deviation from exponential decay and increases in the concentration of polypeptide material in both foam and foam drainage. Analysis of the amino acid composition of whole collapsed foams suggested that polypeptides of enhanced hydrophobicity were selectively partitioned to the gas-liquid interface at foam formation and subsequent consolidation. Estimates of the changes in total mass of the liquid phase within dispensed beer foam suggested that foam collapse proceeded by two distinct stages of exponential decay characterised by different rates (k(1), k(2)). The first rate (k(1)) corresponded to the initial stage of foam collapse and accounted for 85-90% loss of foam mass. This was followed by a slower rate of collapse (k(2)) which corresponded to the consolidation stage. The results from physical and compositional analyses suggest that the initial stage of foam collapse is dominated by gravitational drainage from a liquid rich foam followed by a change in emphasis to coalescence and bubble rupture during the consolidation and residual stages of foam collapse. These findings contribute to the understanding and characterisation of foam formation and stability. (C) 1999 Published by Elsevier Science S.A. All rights reserved.