The study of microbial interactions often requires fastidious and sometimes expensive analytical methods. A reactor specifically designed to carry out studies of interacting populations was developed. Its basic principle consists in keeping both strains of the mixed culture separate by the way of a porous membrane, allowing substrates and metabolites to pass through. As the different strains grow separately, they can be sampled and analyzed distinctly. The culture medium is shared by both strains, and interactions between them occur as if they were mixed in the same vessel. A specific application in winemaking killer yeast interactions is described. The membrane bioreactor made it possible to carry out mixed killer/sensitive fermentations with a double physiological characterization of both killer and sensitive strains.