The stability of beta-glucosidase immobilized on chitosan pellets was studied under operational conditions in continuous stirred tank membrane reactors. The rate of enzyme deactivation was monitored at 25 degrees C using p-nitrophenyl beta-D-glucopyranoside as model substrate. The medium was also supplemented with chemicals present in the wines, namely fructose, ethanol, nerol, linanol and geraniol. Fructose did not decrease biocatalyst stability, while alcohol affected enzyme half-life from 2586 h at 3% (w/v) ethanol to 1378 h at 12% (w/v). The addition of terpenols to solution containing 10% (w/v) alcohol reduced the half-life by a further 10%. Enzyme stability was not dependent on substrate concentration and was considered satisfactory for an industrial process (half-life 1.2 years). These results were independent of the use of wet stored pellets or of samples freeze-dried (24 h at -60 degrees C). No added chemical influenced enzyme specific activity up to the tested limits: fructose 20 mM, terpenols 5 ppm each, ethanol 12% (w/v).