Beer polypeptides and silica gel: Part I. Polypeptides involved in haze formation

Beer contains approximately 500 mg/L protein depending on the brewing procedures employed. This protein is in the form of polypeptides, the majority of which lie within the 10-40 kD size range. Some of these polypeptides are responsible for causing colloidal haze, others enhance foam stability and the remainder appear to have no function in beer except to contribute to mouth-feel. The polypeptides responsible for haze formation are those that can combine with polyphenols to produce a visible cloudy haze. This is undesirable as it can have a negative effect on the beer's shelf life. One way to reduce this effect is to remove these polypeptides using silica gels. It is important that this removal is selective, and the desirable foam enhancing polypeptides are not removed. Data will be presented to show that beer polypeptides are glycosylated and that silica preferentially adsorbs glycoproteins, particularly those with protein components rich in the amino acid proline. The molecular size and composition of glycoproteins recovered from untreated beer, cooked adjunct, silica exposed to beer and beer aged for one year are presented. Glycoproteins involved in foam, and the apparently functionless polypeptides, will be discussed in a subsequent paper.