INTERACTIONS OF PROTEOSES AND POLYPHENOLS IN WORTS, BEERS AND MODEL SYSTEMS

Abstract

Four high-molecular weight proteose fractions from beer were precipitated to varying extents by four different tannin fractions, as shown turbidimetrically in a simple assay. According to this test the most acidic proteose fraction reacted least with all four tannins and the formation of insoluble proteose-tannin complexes was strongly dependent on pH. Moreover, tannins obtained from hops displayed greater tanning power with beer proteoses than did either a tannin isolated directly from barley or one prepared by aerial oxidation of barley prodelphinidin B3. The different reactivities of tannins to proteoses, however, did not correlate well with their reactivities to cinchonine sulphate (CS). Whereas the amounts of break precipitated on boiling a wort moderately were related to the amounts of hop tannins added, barley flavanols had little effect on break formation. In beer, about 50% of the proteoses were of low molecular weight (< 10,000 Daltons) and some were complexed with flavanols. In contrast, isolated fractions of high molecular weight beer proteoses (MW > 10,000 Daltons) were not associated with flavanols. The most acidic of these proteoses were the least stable in solution, being precipitated from beer by down-shifts in pH. The tanning power of unstabilised beer as measured by reaction with cinchonine sulphate was shown to arise from the cumulative effects of at least four different beer components, which should be considered when interpreting the effects of different haze-stabilisation treatments.