Effects of β-glucans and environmental factors on the viscosities of wort and beer

Abstract

This paper reports on the influence of molecular weight and concentration of barley β-glucans on the rheological properties of wort and beer. Environmental conditions such as pH, maltose level in wort, ethanol content of beer, shearing and shearing temperature were also examined for their effects on wort and beer viscosities. In the range of 50-1000 mg/L, β-glucans increased solution viscosity linearly with both molecular weights (MW) of 31,137, 250, 327, and 443 kDa and concentration. The influence of MW on the intrinsic viscosity of β-glucans followed the Mark-Houwink relationship. Shearing wort and beer at approximately 13,000 s-1 for 35 s was found to increase the wort viscosity but reduce beer viscosity. Shearing wort at 20°C influenced β-glucan viscosity more than shearing at 48°C and 76°C whereas the shearing temperature (0, 5 and 10°C) did not effect the viscosity of beer. At lower pHs, shearing was found to reduce the viscosity caused by β-glucans in wort but had no effect in beer. Higher concentrations of maltose in wort and ethanol in beer also increased the viscosity of β-glucan polymers. It was found that β-glucans had higher intrinsic viscosities in beer than in wort (5°C), and lower critical overlap concentrations (C*) in beer than in wort.