Upon ultrasonic treatment at 20 kHz, protein aggregates in a dairy whey solution were broken down. In addition, when sonication was applied to a heated solution of denatured and aggregated proteins, there was a dramatic reduction in viscosity and aggregate size, which was maintained after re-heating. This observed heat stability may be due to shear forces that are induced by acoustic cavitation. To determine whether high shear mixing or homogenisation is able to cause similar effects to that of acoustic cavitation, sonication, high shear mixing and homogenisation were performed on 5 wt% whey protein concentrate solutions at identical energy density levels, which was based on the power drawn in each system. Homogenisation provided similar particle size and viscosity reductions as sonication while high shear mixing was less efficient in decreasing particle size. Cavitation was shown to be absent in both the mixing and homogenisation configurations, indicating that the shear forces generated are responsible for the observed particle size and viscosity reduction. In addition, heat stability was achieved in all systems indicating that a combination of heat treatment and any method that generates high shear forces can be used to improve the heat stability of whey proteins.