Effect of protein-polyphenol ratio on the size of haze particles

Various concentrations of the haze-active (HA) protein gliadin and the HA p olyphenol tannic acid were combined in pH 4.5 buffer. The resulting hazes w ere measured by light scattering, and their particle size distribution patt erns were examined with a laser diffraction particle size analyzer. The sha pe of the haze intensity response generally followed that seen in previous experiments, but haze intensity was noticeably greater with two particular gliadin-tannic acid ratios (2:1 and 5:1, w/w) than with other combinations. The size of the particles varied with the protein-polyphenol ratio, as pre viously hypothesized. In general, larger particles were seen with intermedi ate ratios, while both higher and lower proportions resulted in smaller par ticles. The data expressed as volume percent were highly quantized-essentia lly, only three particle sizes were seen. The proportions of these varied a s the amounts of protein and polyphenol changed. The contributions of parti cles of each size to the haze intensity in different samples were estimated . The results suggested that the particles that contributed the most haze w ere typically in a narrow band, with diameters in the range of 10-20 mu m. Variations in particle size induced by normal brewing practices are expecte d to have an impact on fining and filtration performance.