Cleaning of whey protein fouled surfaces occurs by cleaning chemical diffusing into the deposit, causing swelling of the deposit into a form which is capable of being removed by fluid shear. The mechanisms ongoing during cleaning have been studied in a series of experiments in which pilot scale plate heat exchangers (PHE) and small disks are cleaned by pulses of chemical and water. Observation of the pressure drops during cleaning of plate heat exchanger sections shows that diffusion and removal can be separated; the pressure drop increases when water replaces chemical, suggesting that sodium hydroxide already in the deposit is still causing swelling. Rinsing can remove swollen deposit; that might reduce the impact of cleaning on the environment. An estimate of the kinetics of the process can be made by studying the partial removal of deposit on small disks, using heat flux sensors to measure thermal recovery.