Investigation of intermittent air exposure on four-stage and one-stage anaerobic semi-continuous mixed-acid fermentations

► Anaerobic mixed-acid countercurrent fermentations in minimal and high oxygen conditions. ► Difficult to maintain anaerobicity in commercial-scale fermentations. ► Oxygen exposure might decrease performance of commercial-scale fermentations. ► Fermentations had similar yields, conversions, selectivities, and bacterial profiles. ► Minimal oxygen fermentations had more high-molecular-weight carboxylic acids.