The Effect of Beer pH on Colloidal Stabilization with Adsorbents

摘要

Solutions of the haze-active (HA) protein gliadin were prepared in buffer at different pH's and treated with silica. Analysis using the bicinchoninic acid and HA protein methods produced similar patterns, with greater protein removal near pH 3.5 and 5.0. Portions of an unchillproofed beer were adjusted to different pH's, treated with silica, and subjected to HA and foam-active (FA) protein analyses. The HA protein results showed greater protein removal near pH 3.8 and least removal near pH 4.4. FA protein was hardly affected, although slightly more was removed near pH 4.4. Tan-nic acid (TA) and catechin were each combined with soluble polyvinyl-pyrrolidone in buffer solutions with different pH's, and turbidity was determined after incubation. TA formed maximum haze near pH 4, while catechin formed more haze above pH 5. Portions of unchillproofed beer were adjusted in pH and treated with polyvinylpolypyrrolidone (PVPP). The treatment pH had essentially no effect on total polyphenol removal. HA polyphenols were removed to a greater extent near pH 3.8 and 4.6, with lower effectiveness at intermediate pH's. The colloidal stabilization performance of both silica and PVPP was better at pH's near the extremes of the beer pH range. This may account for difficulties encountered in stabilizing some beers.