There is limited information available on quantifying the operability of continuous ultrafiltration plants used for the production of whey protein concentrates. Based on modelling of the process, the operability studies demonstrate that a standard 12 loop commercial ultrafiltration plant is able to produce the desired specifications of the concentrates. The studies also indicate that mid-run washing of the plant is necessary to reduce the effects of long-term membrane fouling. Although it becomes more difficult to achieve the desired product flowrate as protein concentration in the feed increases, proper knowledge of process variations makes it possible to compensate for the effects from fluctuations in whey composition in order to maintain the desired specifications of the concentrates. (c) 2007 Elsevier B.V. All rights reserved.