Commercial enzymes differ in their content of beta-glucanases and xylanases and, in their ability to reduce mash viscosity and increase extract. No simple relationship exists between measurable enzyme activity and these parameters, suggesting that the benefit of these enzymes in mashing is not simply predicted from absolute levels of enzyme, reinforcing the view that enzyme efficacy should be evaluated directly in mashes. Preparations comprising principally xylanase increase wort viscosity when added in lower levels to mashes, probably by releasing beta-glucan from its entrapment by arabinoxylan within the cell walls of barley. The glucanases have greater impact than xylanases on viscosity. Combinations of xylanase and beta-glucanase have the greatest impact on viscosity and extract yield. (c) 2005 Elsevier Inc. All rights reserved.