Mechanisms of Beer Colloidal Stabilization

The effects of treatments that influence beer colloidal stability on foam-active protein and haze-active protein and polyphenols were studied. Unchillproofed beer was treated with bentonite, silica gel, and polyvinylpolypyrrolidone (PVPP). Bentonite adsorption removed both haze-active and foam-active protein. Silica gel adsorption removed haze-active protein but almost completely spared foam-active protein. This specificity results because silica gel binds to the proline residues in the protein; these are the same sites where polyphenols attach to create haze. As a result, only those proteins that can participate in haze formation are affected. PVPP removed approximately half of the haze-active polyphenol from beer but had little effect on foam-active or haze-active protein. Fining with gelatin greatly reduced the level of haze-active protein in the beer. Fining with tannic acid reduced the level of haze-active protein and, at higher addition rates, the concentration of haze-active polyphenol. Theoretical aspects of enzymatic chillproofing were considered. Since phenylalanine and tryptophan are present in hordein but not the foam-active barley lipid transfer protein 1 (LTP1), it is theoretically possible that an enzyme could be found that would attack haze-active but not foam-active protein.