Pervaporation is an alternative to distillation for recovering ethanol produced by fermentation of grains and biomass. Ethanol-selective mixed matrix membranes of the hydrophobic zeolite ZSM-5 in polydimethylsiloxane (PDMS) have superior performance compared to pure PDMS membranes in pervaporation of clean ethanol/water solutions, but are susceptible to performance reduction when pervaporating fermentation broths. The effects of pervaporating a variety of solutions with 60 wt% ZSM-5/PDMS membranes were studied. Corn dry-grind fermentation broth, thin stillage, and a synthetic syngas fermentation broth rapidly and significantly degraded mixed matrix membrane performance. Broths treated to remove corn oil and fatty acids were much more benign. Oleic acid, as a representative fatty acid, was identified as a significant performance reducer. Published by Elsevier B.V.