Formation of Protein−Polyphenol Haze in Beverages

Protein−polyphenol hazes form in beer, wine, and fruit juices and can limit shelf life. Haze-active protein is higher in beer than the other beverages. Haze-active polyphenol is highest in apple juice and red wines, variable in grape juices, and low in beer and white wine. A systematic study of factors that influence haze formation was carried out in a model system. Pectin, arabinogalactan, and poly(galacturonic acid) led to increased haze while free amino acids and other carbohydrates had no effect. Maximum haze occurred near pH 4 with less haze at higher and lower pH's. As ethanol concentration increased near pH 4, the haze at first declined, but further increases in ethanol led to increased haze. It appears that haze formation is similar in all the beverages examined and may be explained by a single mechanism. This has implications for analysis of haze-active constituents and beverage stabilization. Keywords: Haze-active protein; haze-active polyphenol; pH; alcohol; turbidity; beer; wine; fruit juices