Beer Polypeptides and Silica Gel
Part II. Polypeptides Involved in Foam Formation

Kenneth A. Leiper, ¹ Graham G. Stewart ¹, ³ and Ian P. McKeown ^2
1International Centre for Brewing and Distilling, Heriot-Watt University, Riccarton, Edinburgh, EH14 4AS, Scotland.
²Ineos Silicas Ltd, Liverpool Road, Warrington, WA5 1AB, England.
³Corresponding author. E-mail: G.G.Stewart@hw.ac.uk

J. Inst. Brew. 109(1), 73-79, 2003  |   VIEW ARTICLE

ABSTRACT
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, some enhance foam stability and the remainder appear to have no function in beer except to contribute to mouthfeel. Those polypeptides involved in haze formation were described in a previous paper. To continue these studies, data is presented to show that foam polypeptides are highly glycosylated and that purified foam glycoprotein contains low levels of the amino acid proline. As silica preferentially adsorbs polypeptides rich in proline, it is unlikely to adsorb this material and damage foam stability. The molecular sizes and composition of glycoproteins recovered from untreated beer, purified foam and beer from which the foam component has been removed are presented. These fractions include the polypeptides responsible for foam stability and those that appear to have no role in physical stability.

Key words:
Amino acids, beer stability, carbohydrates, foam, polypeptides, silica gel.

Publication no. G-2003-0310-089  ^© 2003 The Institute & Guild of Brewing