Bacillus coagulans spores were immobilized in polyvinylalcohol (PVA) hydrogel, lens-shaped capsules known as LentiKats. The immobilized spores were used in an anaerobic, non-sterile process in the repeated batch fermentations at 50 degrees C and produced lactic acid at 7.4 g l(-1) h(-1), which was double that of the free cell system. No mechanical deformation of the capsules and no contamination were observed.