A process for obtaining a constituent, such as whey protein isolate, from whey protein concentrate by microfiltration. Retentate is fed to a microfiltration arrangement (4) where at a first stage (see 5.1, figures 2(a) & 2(b)) the retentate stream is separated into a first fat enriched substream (see 255, figure 2(b)) and a first fat depleted substream (see 256, figure 2(b)). The first fat depleted substream is then fed to a second stage (see 5.2, figures 2(a) & 2(b)) where the first fat depleted substream is further separated into a second fat enriched substream and a second fat depleted substream. A recirculated substream (see 14, figure 2(b)) is then fed from the second or both the first and second fat depleted substreams back to the microfiltration arrangement. The two stage separation process, followed by recirculation of the fat depleted retentate, advantageously enhances the quality and yield of the end constituent.
