Characterization of Haze-Forming Proteins of Beer and Their Roles in Chill Haze Formation

Four proteinaceous fractions responsible for chill haze of beer (haze-forming proteins I, II, III, and IV) were isolated from beer by ultrafiltration followed by ammonium sulfate precipitation, ion-exchange chromatography, and gel chromatography. The haze-forming proteins, constituting about one third of the nitrogenous substances of beer, had molecular weights of 1,000 to 40,000 and contained appreciable amounts of proline. The haze-forming proteins, particularly fraction II, had high affinities for polyphenols and readily combined with polyphenols to form chill haze. Because the contents of proline in the haze-forming proteins correlated well with their affinities for polyphenols, proline must be important in the combination of haze-forming proteins with polyphenols. Hydrogen bonding or hydrophobic bonding or both seemed to be involved in the combination. Immunological studies showed that the haze-forming proteins originated mainly from malt hordein and were mainly responsible for chill haze of beer.