Pervaporation was used to concentrate acids, esters and ketones in model flavour mixtures. The characteristics of the feed mixture (pH and presence of dairy ingredients) were found to alter the pervaporation behaviour of the flavour compounds. This effect was partially due to a reduction in driving force (caused by a lower activity in the aqueous phase as evidenced by the mole fraction in the headspace above the feed), and partially due to the sorption and diffusion behaviour of the flavour compounds. Acids were concentrated most effectively at pH 3.5 or below, when they were in their undissociated forms; their enrichment factors were reduced by up to 84% when the pH was increased to 7. Milk fat reduced the pervaporation enrichment of flavour compounds by up to 95%, as the flavour compounds partitioned into the fat phase and hence did not pass through the membrane as easily. In the presence of either milk protein isolate or lactose, enrichment factors were reduced by 45-67% for short-chain esters and ketones, for which permeation through the membrane was limited by the sorption step. (C) 2011 Elsevier Ltd. All rights reserved.