beta-glucans have been implicated in many process problems in the brewery including slow lautering, lowered rates of beer filtration, and haze development in storage. The objective of this study was to test the hypothesis that, "wort and beer filterability is dependent on the molecular weight (MW) and concentration of beta-glucan polymers". The effect of shearing of wort and beer on the MW/particle size distribution of beta-glucans and their contribution to the apparent viscosity and turbidity was also examined. Both high gravity wort (16% extract) and a high gravity degassed beer were treated with a commercial beta-glucanase preparation to reduce the beta-glucan concentration to a negligible level. Following beta-glucanase denaturation, beta-glucans with MW's of 31, 137, 250, 327 and 443 kDa at 50, 100, 200, 400, 600, 800 and 1000 mg/L were added to the treated wort (final extract 12%) and beer (final ethanol 5%). The samples were sheared and their properties compared with un-sheared controls. A small-scale lautering device was built up to perform constant pressure (1.5 kPa) lautering tests. Wort and beer samples were filtered (@ 20 and 0 C, respectively) using a constant pressure membrane (0.45 micrometer pore size) filtration apparatus. Results indicated that higher polymer MW and beta-glucan concentration led to higher viscosity, turbidity and filtration resistance values (p<0.001) in an interdependent fashion (p<0.001). That is, the effect of concentration varied with MW of the added beta-glucan polymer. It was also discovered that shearing of the samples significantly increased their viscosity, turbidity and the resistance to filtration (p<0.001). In order to explain these findings, a size exclusion membrane filtration technique was developed to categorize the apparent particle size of beta-glucan aggregates into >0.45, 0.1-0.45, 0.01-0.1 and <0.01 micrometer classes. It was found that shearing of the beta-glucan dispersions increased beta-glucan particle size. Particularly, the 0.01-0.1 micrometer size fraction increased while that of the <0.01 micrometer size fraction decreased (p<0.001). However, the proportion of >0.1 micrometer fraction did not change (p>0.05) after shearing and the amount of >0.45 micrometer species was negligible. Findings suggested that the data could be modelled by Poiseuille's law, (i.e., the flow rate was controlled by the viscosity of the filtrate). Shearing of samples retarded filtration by increasing particle size (and therefore increasing viscosity). Apparently, beta-glucans smaller than 443 kDa are not involved in the fouling of the 0.45 micrometer membranes in beer filtration.