The effect of apple cider characteristics and membrane pore size on membrane fouling

Microfiltration (MF) of apple cider using four membrane pore sizes was investigated. MF with 0.2 and 0.45 μm pore sizes, and with 0.8 and 1.4 μm pore sizes, respectively, resulted in similar flux behavior and MF juice characteristics. Clear juice was obtained using all four pore sizes. MF did not cause any significant changes in pH and °Brix, regardless of pore size. Viscosity of the MF juice was lower than of the unfiltered apple cider for all membranes, but the viscosity decrease was the largest for the 0.2 and 0.45 μm membranes, due to the low transmission of pectin into the MF juice. Pectin transmission was 3-9% of the initial pectin content for the 0.2 μm membrane, 6-51% for the 0.45 μm. 45-100% for the 0.8 μm, and 60-100% for the 1.4 μm membrane. Apple cider haze particles that were smaller or of size comparable with the membrane pore size were deemed responsible for fouling, while particles much larger than the pores did not have a significant contribution to fouling. The fouling of 0.2 μm and 0.45 μm membranes was dominated by cake layer formation (external fouling), while fouling of the 0.8 μm and 1.4 μm membranes was dominated by pore constriction and pore blocking (internal fouling).