There is a general lack of information on large scale operation of an immobilised enzyme reactor with realistic production capacity. In the current study, beta-galactosidase from Kluyveromyces lactis was immobilized on cotton fabric using glutaraldehyde as the cross-linking reagent. A pilot-scale module with a 10-l packed-bed reactor has been set up and applied to hydrolyse lactose in whole milk. Both batch and continuous runs have been accomplished. About 95% of lactose conversion was achieved after 2 h of batch operation. The extent of the lactose hydrolysis and the productivity of the reactor changed with the residence time in continuous operation mode. The experimental data have also been compared with simulation results using a kinetic model developed with the small packed-bed module previously by the same research group. (c) 2006 Elsevier B.V. All rights reserved.