Uninvestigated control factors of meta-fermentation, the fermentative production of pure chemicals and fuels in a mixed culture system, were examined for production of optically pure L-lactic acid (LA) from food waste. In meta-fermentations by pH swing control, L-LA production with 100% optical purity (OPLLA) was achieved even using unsterilized model kitchen refuse medium with preferential proliferation of L-LA-producing Bacillus coagulans, a minor member in the seed, whereas agitation decreased OPL-LA drastically. pH constant control shortened the fermentation time but decreased OPL-LA and LA selectivity (S-LA) by stimulating growth of heterofermentative Bacillus thermoamylovorans. Deliberately switching from pH swing control to constant control exhibited the best performance for L-LA production: maximum accumulation, 39.2 g L (1); OPL-LA, 100%; S-LA, 96.6%; productivity, 1.09 g L (1) h (1). These results present a novel pH control strategy for efficient L-LA production in meta-fermentation based on a concept different from that of pure culture systems. (C) 2016 Elsevier Ltd. All rights reserved.