A process was developed for the production of polygalacturonase (poly-1,4-α-d-galacturonide glycanohydrolase, EC 184.108.40.206) by Aspergillus niger VTT-D-77050 and its mutant VTT-D-86267. High levels of production were obtained in laboratory fermentations on a beet extraction waste medium. The yields were lower in pilot scale production experiments, although the producing strains were stable in the process conditions. The enzyme mixture produced in one pilot fermentation was used successfully for improving the cloud stability of fruit nectars. In addition to polygalacturonase, the preparation also contained appreciable levels of some other important activities.