Membrane separation processes have great potential in the food industry due to their ability to operate in mild conditions and to involve no phase change or chemical agents. The present work is part of a project which investigates the use of integrated membrane processes to produce fruit juices that are additive-free and have a natural, fresh taste. A study to optimize the depectinization and clarification of apple juice by enzyme membrane reactors has been carried out by using laboratory and semipilot scale equipments. The performance of the membrane systems has been investigated in terms of permeate flux and degree of depectinization. The effects of various parameters (transmenbrane pressure, axial flow rate, feed mixture, etc.) on membrane fouling have been evaluated, and the fouling mechanism has been interpreted in terms of complete pore blocking or cake filtration. The permeate flux improved with an increasing enzyme percentage in the feed mixture.