Turbidimetric Titration of a Haze-Active Polyphenol in Beer

Abstract

At least two commercial instruments that perform automated turbidimetric titrations are available for determining haze-active (HA) constituents in beer. They have advantages over single-point measurements due to the interactions between beer HA polyphenols, HA proteins, and other beer constituents. Analysis of HA polyphenols is particularly difficult due to their low concentration in beer. Manual turbidimetric titrations with soluble polyvinylpyrrolidone (PVP) were carried out in model systems with a HA polyphenol (tannic acid [TA]), a non-HA polyphenol (epicatechin), a HA protein (gliadin), and a non-HA protein (lysozyme). Increasing concentrations of TA resulted in higher turbidity peaks at higher titrant volumes. Essentially no haze was seen with epicatechin or lysozyme. Gliadin solutions had an initial modest haze that decreased with increasing titrant. The effects of adding fixed amounts of epicatechin, lysozyme, or gliadin to TA were examined. In the presence of epicatechin or lysozyme, the titration endpoints were shifted higher. The endpoints with mixtures of gliadin and TA were similar to those found with TA alone. PVP titration also was applied to samples of unchillproofed beer treated with different amounts of silica or polyvinylpolypyrrolidone and showed responses of the expected magnitudes.