Cell‐recycle membrane bioreactor for conducting continuous malolactic fermentation

A cell‐recycle membrane bioreactor system has been evaluated for conducting rapid, continuous malolactic conversion in wine. A reactor (300 mL) containing 10 10 cfu/mL of Leuconostoc oenos and 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 of Leuc. 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 of Leuc. oenos and Saccharomyces cerevisiae .