Hydrophobic pervaporation is rarely considered in the biotech industry despite several potential advantages and some applications. This is related to fact that the majority of studies have been with binary feed systems, while real feed mixtures are often multi-component and might contain impermeable components, such as salts and sugars. In order to successfully optimise hydrophobic pervaporation, it is essential to understand the influence of impermeable components. Three impermeable components (NaCl, MgCl 2 , and glucose) were studied for their effect on the permeation of water and 1-propanol through two commercially available pervaporation membranes (Pervap 1060 and 1070). From the experiments, it was found that the addition of salts and sugars increase the selectivity of 1-propanol to water in the order MgCl 2 > NaCl > glucose. The results were compared with literature data on the addition of other components such as citric acid, acetic acid, glycerine and Na 2 SO 4 . Based on these results, two main mechanisms by which permeation is affected were identified: (1) change in activity coefficient due to third component, and (2) fouling and penetration of the membrane by impermeable components. The former factor tends to increase flux of the organic compared with a binary mixture whilst the latter acts to decrease flux. The overall conclusion is that impermeable components can influence the performance of pervaporation significantly.