A packed bed reactor (PBR) design was tested for the purpose of continuous pectinase production with yeasts, as a possible alternative to the traditional batch process using fungal cultures. Two different carriers - a porous glass (Siran) and a cellulosic carrier obtained from spent grains (barley) - were used to immobilize Kluyveromyces marxianus CCT 3172, a yeast strain secreting endopolygalacturonase. To improve cell distribution throughout the column, part of the outflow was recycled. Cell loads of 0.204 and 0.247 g(biomass)/g(carrier) were obtained at the top and bottom of the PBR with spent grains, respectively. Using the PBR with Siran as the immobilization support, 0.071 g(biomass)/g(carrier) was the biomass load at the top of the column while at the bottom a value of 0.147 g(biomass)/g(carrier) was found. The highest value for pectinase volumetric productivity (Pv = 1.68 U/ml h) was achieved in the PBR with Siran for a D = 0.260 h(-1) and a glucose concentration on the inlet of S-in = 40 g/l. Both carriers were suitable for pectinase production. The best results were obtained with a high and uniform biomass concentration in the column, together with high dilution rates and total glucose consumption. (c) 2004 Elsevier Ltd. All rights reserved.