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 mouthfeel. 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.Key words: Amino acids, beer stability, carbohydrates, mashing, polypeptides, silica gel.
-2863(9'8-32It has been known for many years that silica gel is an effective beer stabilizer as it selectively removes those polypeptides that are responsible for causing haze formation. However, it is not clear what size of polypeptides are involved and what proportion of total beer protein they constitute. Also, it is not clear to what extent silica structure effects the ability to adsorb haze-causing polypeptides.Beer contains approximately 500 mg/L protein. Most of this is in the form of polypeptides that are in the 5-100 kD size range. Due to the combined hydrolytic and destructive effects of malting, mashing, boiling and fermentation, there is a very small range of polypeptides present in beer. Three major components have been identified, a polypeptide of 40 kD known as Protein Z 9 , a polypeptide of 9.7 kD known as LTP1 19 which is involved in foam stability, and a group of polypeptides that range between approximately 10 kD to 30 kD. These originate from barley hordein, are rich in the amino acids proline and glutamic acid and are involved in haze formation 3 .The formation of permanent haze occurs when the proline-rich polypeptides combine with specific polyphenols, particularly the flavanol dimers procyanidin B3 and prodelphinidin B3 17 . This haze forming reaction can be prevented by removing either the protein component with silica gel, or the polyphenol component with PVPP (polyvinylpolypyrrolidone).Silica gel (SiO 2 ) is a highly porous structure with a large surface area. Its surface is covered with silanol (SiOH) groups that bind to proline residues in polypeptides. Silica is highly selective for haze protein due to the high levels of proline present in these polypeptides...