Ambiguous Impact of Wheat Gluten Proteins on the Colloidal Haze of Wheat Beers

Abstract

Laboratory-scale brews were prepared from barley malt with various addition levels of commercial wheat gluten. These were calculated to range from 0 to 150% of the amount of gluten in a typical wheat beer mash (60% barley malt and 40% unmalted wheat). Nephelometric permanent haze readings of the experimental beers showed an increase of the haze intensity with the increasing gluten levels, reaching a maximum of 50 EBC haze units at the gluten level corresponding to the wheat gluten level in a mash based on 88% barley malt and 12% wheat. At higher gluten levels, the haze intensity declined to values lower than 1 EBC haze unit. In contrast, the polyphenol levels of centrifuged beers decreased continuously with increasing gluten additions. Total polyphenol, total flavanoid, and simple flavanoid levels decreased by as much as 17, 23, and 21%, respectively. Haze intensities of laboratory-scale beers brewed with variable levels of two wheat varieties with different protein levels were higher for 5% wheat inclusion than for the reference all-malt beer. However, at higher wheat levels (from 10% onward), the haze intensity decreased continuously to 1 EBC haze unit at 40% wheat. Beer brewed with low-protein (12.6%) wheat contained systematically more permanent haze than did beer brewed with high-protein (14.7%) wheat. It was concluded that wheat gluten proteins interact with polyphenols, resulting in the formation of a haze or precipitate depending on the gluten concentration.