Abstract 069
The effect of protein/polyphenol ratio on the size of haze particles
J. Amer. Soc. Brew. Chem. 58 (3): 117-123, 2000
K.J. Siebert and P.Y. Lynn
Various concentrations of the haze-active (HA) protein gliadin and the HA polyphenol tannic acid were combined in pH 4.5 buffer. The resulting hazes were measured by light scattering and their particle size distribution patterns were examined with a laser diffraction particle size analyzer. The shape 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 previously hypothesized. In general larger particles were seen with intermediate ratios, while both higher and lower proportions resulted in smaller particles. The data expressed as volume % were highly quantized – essentially only three particle sizes were seen. The proportions of these varied as the amounts of protein and polyphenol changed. The contributions of particles of each size to the haze intensity in different samples were estimated. The results suggested that the particles that contributed the most haze were typically in a narrow band with diameters in the 10-20 µm range. Variations in particle size induced by normal brewing practices are expected to impact fining and filtration performance.
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