The reverse osmosis (RO), as alternative to the chaptalization or vacuum evaporation, enables the must concentration if sugar concentration needs to be increased. The presented study shows the incidence of operating parameters of a RO industrial system to the quality of extracted water and to the enological impact of the concentration. The low temperature, about 10degreesC and high applied pressure, about 75. 10(5) Pa, are conditions that prevent the must components to cross the membrane. Meanwhile, a high pressure may provoke the. tartaric acid precipitation at the membrane surface. That precipitation depends also on the Volume Reduction Factor (VRF). The fouling is essentially function of must preparation, spacer geometry and applied pressure. The musts obtained by RO are of good quality, but this technique should not be used in palliation of lack of fruit maturity.