The relationship of beer high molecular weight protein and foam.

Siebert, K.J. and Knudson, E.J.

Abstract
Although it has long been known that the foam quality of beer is related to its protein content, it has only more recently been discovered that the proteins involved constitute a specific fraction of the range of beer proteins, and are quite different both from the hordeins (the major barley protein group, also found in malt and beer) and from the fraction causing proteinaceous haze. The Kjeldahl test (the usual measure of malt or beer protein content) which indicates the total amount of combined nitrogen and therefore of nitrogenous compounds (including nucleic acids and other non proteins) is therefore not a reliable measure of foam quality. Since the foaming proteins are all large molecules (10000 Daltons or more) a size selective test is more reliable in this context. The authors found a very close correspondence between the results of the Coomassie blue stain test (which detects large proteins of above 5000 Daltons) and of the Rudin and NIBEM foam stability tests on the same beer. Since the Coomassie test is known to be very much more sensitive to proteins containing certain specific amino acids than to other proteins of similar molecular size, the fact that the foaming proteins are much richer in those amino acids than other beer proteins is considered a good explanation for this relationship. Experiments are described in which the factors affecting the foaming protein content of beer were studied. It was concluded that the determining factors were the foaming protein content of the malt and the losses thereof during the brewing process, particularly mashing. All malt beers are usually richer in foaming proteins than those brewed using significant quantities of adjuncts, as most commonly used adjuncts contain no such proteins.
Keywords : amino acid analysis beer foam stability malt molecular weight protein sensitivity stain