Destabilization of beer foam by lipids: Structural and interfacial effects

Mechanisms in which fatty acids destabilize beer foam have been studied. Foam stability of a pilot-brewed beer was measured in the presence of a range of concentrations of fatty acids, similar to those found in a range of commercial beers. The foams were sparged with nitrogen and studied using a microconductivity technique. The fatty acid chain length varied from C(6) to C(18), C(18:1), and C(18:2). While C(6) to C(10) fatty acids had no impact on the foam stability over the concentration range studied, the longer-chain fatty acids were more destructive. Thus, C(12) to C(14), C(18:1), and C(18:2) reduced foam stability and the surface elasticity of beer. These data suggest that the fatty acids adsorbed into the protein-stabilized surface weakened the adsorbed film, resulting in an increased probability of coalescence. The saturated fatty acids, C(16:0) and C(18:0), damaged the foam very effectively but did not influence the surface rheology. Light-scattering experiments showed increased numbers of aggregates in these samples, suggesting that these fatty acids destabilized beer foam through a mechanical film-bridging mechanism, similar to that used by particulate antifoam systems.