Abstract 054
Mechanisms of beer colloidal stabilization
J. Amer. Soc. Brew. Chem. 55: 73-78, 1997
K. J. Siebert and P.Y. Lynn
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.
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