Studies on the physical and compositional changes in collapsing beer foam

Batches of foam were characterised by analysis of conductivity and quantita tive changes in mass and solute composition of material retained both withi n foam and foam drainage. The conductivity of dispensed beer foam declined exponentially during the initial stages of foam collapse, followed by a sec ondary or consolidation stage characterised by deviation from exponential d ecay and increases in the concentration of polypeptide material in both foa m and foam drainage. Analysis of the amino acid composition of whole collap sed foams suggested that polypeptides of enhanced hydrophobicity were selec tively partitioned to the gas-liquid interface at foam formation and subseq uent consolidation. Estimates of the changes in total mass of the liquid ph ase within dispensed beer foam suggested that foam collapse proceeded by tw o 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 sta ge. The results from physical and compositional analyses suggest that the i nitial stage of foam collapse is dominated by gravitational drainage from a liquid rich foam followed by a change in emphasis to coalescence and bubbl e rupture during the consolidation and residual stages of foam collapse. Th ese findings contribute to the understanding and characterisation of foam f ormation and stability. (C) 1999 Published by Elsevier Science S.A. All rig hts reserved.