The aims of this study were to compare the new pilot plant filtration results of grape juice with the laboratory experiments [A. Rektor, N. Pap, Z. Kokai, R. Szabo, Gy. Vatai, E. Bekassy-Molnar, Application of membrane filtration methods for must processing and preservation, Desalination 162 (2004) 271-277], beside that the selective removal of water from grape juice, to increase its sugar content. Experiments were carried out using a pilot size reverse osmosis (RO) apparatus with 0.6 m(2) flat sheet membrane area. The membrane was MFT-Koln RO type, the apparatus was built by the Hidrofilt Ltd. Grape juices, originated from different wine-yards, were concentrated. The influence of transmembrane pressure and temperature on the sugar content and concentration time were measured. (C) 2006 Elsevier B.V. All rights reserved.