Both systems operating in cross-flow mode are shown in Fig. 2. The
permeate flux at the start of the batchwisefiltration of vat milk with 3.2%
fat running via the MF pilot plant was 81.5 L/hm² at a transmembrane
pressure of 1.1 bar and a feed inlet pressure of 4.35 bar. The viscosity of
the retentate rose as the concentration of the vat milk increased. To
maintain a pumpable consistency of the highly concentrated retentate,
the temperature was raised from DM 14% to 58 °C and from DM 27% to
75 °C until the end of filtration. With increasing concentration of the vat
milk, the transmembrane pressure rose to 3 bar until a minimum
permeate flux of approx. 12 L/hm2 was achieved and filtration could be
completed. In the MF/UF/UF pilot plant the milk was continuously
concentrated to high dry matter contents at a moderate temperature of
50–55 °C. The retentate flow for pasteurized vat milk with a fat content
of 3.2% was 47.73 L/h and had a diafiltration factor (DF) of 0.28. The DF is
defined as the ratio of output quantity to wash water quantity. The
filtration temperature was kept between 50 and 55 °C to avoid protein
denaturation and to guarantee optimum suitability for cheese
production