Abstract 082
Effects of alcohol and pH on protein-polyphenol haze intensity and particle size
J. Amer. Soc. Brew. Chem. 61 (2): 88-98, 2003
K.J. Siebert and P.Y. Lynn
Gliadin (100, 200, 300, 400 and 500 mg/L) and tannic acid (40, 60, 80, 100, 120, 140 mg/L) were combined in buffer model systems at various pHs (4.0, 4.5, 5.0, 5.5, 6.0 and 6.5) and ethanol contents (0%, 6% and 12% (v/v)). Turbidities were determined and particle size analysis was carried out. The maximum turbidity occurred near pH 5.0-5.5 when no ethanol was present, at pH 4.5-5.0 with 6% (v/v) and pH 4.5 with 12% ethanol. The greatest haze intensity at each pH tended to occur when both gliadin and TA concentrations were high. A response surface model was fit through the 540 data points (R = 0.867) and was used to predict haze intensities for other conditions. Under wort conditions (pH 5.5 and 0% ethanol) particles were predominantly small (0.25-1 µm) and medium (5-70 µm) sized. With added ethanol, haze intensity at beer pH and large particles both increased, and at pH 4.5 small particles (<1 µm) increased considerably. The results indicate that the pH and the alcohol content of a beer are likely to influence both the size of colloidal particles and light scattering. This should affect visual turbidity, sedimentation of the beer during storage or centrifugation, and removal of particles by filtration.
Back to K.J. Siebert home page | Back to publication list