Aims: To examine the reliability of membrane cultures as a model solid-state fermentation (SSF) system. Methods and Results: In overcultures of Aspergillus oryzae on sterilized wheat flour discs overlaid with a polycarbonate membrane, we demonstrated that the presence of membrane filters reduced the maximum respiration rate (up to 50%), and biomass and alpha-amylase production. We also show that the advantage of membrane cultures, i.e. total recovery of biomass, is not very evident for the system used, while the changes in metabolism and kinetics are serious drawbacks. Conclusions: The use of membrane cultures is artificial and without substantial benefits and therefore has to be carefully considered. Significance and Impact of the Study: In future studies on kinetics and stoichiometry of SSF, one should not completely rely on experiments using membrane cultures as a model SSF system.