AbstractA cell‐recycle membrane bioreactor system has been evaluated for conducting rapid, continuous malolactic conversion in wine. A reactor (300 mL) containing 1010cfu/mL ofLeuconostoc oenosand operating at a flow rate of 6 mL/min for periods up to 56 h gave greater than 95% degradation of L‐malic acid in a range of red and white wines. Stability of malic acid degrading activity and long term performance of the reactor varied with strain ofLeuc. oenos, wine being processed and temperature. Increasing operating temperature from 20°C to 30°C caused rapid loss of activity. When grape juice was processed, reactor performance (>95% degradation of malic acid) was stable for at least 125 h. Addition of 10% ethanol to the juice caused a loss in reactor activity. Some off‐flavours were acquired by the wine during processing in the reactors, but this problem was minimised by using reactors containing a mixture of cells ofLeuc. oenosandSaccharomyces cer