The slip velocity of potato granule pastes as a function of wall shear stress was determined in capillary flow at several temperatures and aqueous concentrations. The Mooney technique was used together with a variation of the method in which the shear rate for each die was subtracted from that for a no‐slip flow, approximated using rough dies. General agreement between the two methods was found, despite some unrealistic results in applying the Mooney technique. A critical wall shear stress for slip was found, consistent with published results for other materials. The exponent in the wall shear stress–slip velocity power law was consistently higher than that in the wall shear stress–apparent wall shear rate relationship. This is in keeping with the observation that the ratio of slip flow rate to total flow rate fell with increasing wall shear stress.