Fluid dynamic gauging (FDG) has been used to study cake fouling during cross-flow microfiltration of inactive Saccharomyces cerevisiae yeast suspensions through a 5μm nominal pore size mixed cellulose ester membrane. Cake thickness was measured in situ and in real-time during fouling, for which an initial growth rate of ca. 0.81μms -1 was observed at TMP=35mbar and Re duct=1000. The thickness increased asymptotically to a terminal value of 130μm, limited by the FDG process. Although it influences the evolution of the cake thickness, FDG can nevertheless be used to perform strength tests on preformed cakes, by imposing controlled shear stresses to the surface and measuring the thickness following deformation. Cake deformation via incremental increases in shear stress demonstrated that the cake's resilience to tangential fluid shear was inversely proportional to its thickness. It was found that preformed cakes over 250μm thick were deformed by shear stresses <10Nm -2, indicating very loose cohesion between cells on the cake's surface. The range and accuracy of thickness measurements is subject to the strength of fouling layers and the operating conditions of the apparatus. Measures to enhance the technique's efficacy have been identified and are currently underway.