DYNAMIC CHANGES IN THE COMPOSITION AND PHYSICAL BEHAVIOR OF DISPENSED BEER FOAM

Beer foam generated under conditions encountered at dispense was separated from beer, allowed to collapse and sampled at regular intervals. The yield of collapsed beer foam decreased logarithmically with time. Analysis of the composition of collapsed beer foam fractions over a period of time, considered to be relevant to actual consumption of beer (30 minutes) showed that polypeptide material and isomerised alpha acids were selectively partitioned in beer foam. The concentration of total polypeptides, soluble polypeptides, isomerised alpha acids and foam precipitate material in collapsed beer foam, firstly increased with foam collapse time and then approached maximal values. Under these conditions the concentration of polypeptide material and isomerised alpha acids increased 10-30 fold and 7 fold respectively as compared to beer. No evidence was obtained for the preferential partition of purine nucleosides and free bases in foam (adenosine + deoxyadenosine, guanosine + deoxyguanosine, adenine, guanine and xanthine).