In this work, whey protein concentrate (WPC) solutions at different concentrations (22.2, 333 and 150 g L-1) were used to foul three ultrafiltration (UF) membranes of different materials and molecular weight cut-offs (MWCOs): a polyethersulfone (PES) membrane of 5 kDa, a ceramic ZrO2-TiO2 membrane of 15 kDa and a permanently hydrophilic polyethersulfone (PESH) membrane of 30 kDa. NaCl solutions at different salt concentrations, temperatures and crossflow velocities were used to clean the UF membranes tested. The cleaning efficiency was related to the MWCO, membrane material and operating conditions during fouling and cleaning steps. NaCl solutions were able to completely clean the membranes fouled with the WPC solutions at the lowest concentration tested. As WPC concentration increased, the hydraulic cleaning efficiency (HCE) decreased. The results demonstrated that an increase in temperature and crossflow velocity of the cleaning solution caused an increase in the HCE. Regarding NaCl concentration, the HCE increased up to an optimal value. As the concentration was greater than this value, the cleaning efficiency decreased. In addition, an equation that correlates the cleaning efficiency to the operating parameters studied in this work (temperature, NaCl concentration, crossflow velocity in the cleaning procedure and WPC concentration during the fouling step) was developed and then, an optimization analysis was performed to determine the values of the parameters that lead to a 100% cleaning efficiency. (C) 2015 Published by Elsevier B.V.