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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 10°C and high applied pressure, about 75.105 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.

The results of RO concentration obtained with the wines issued from different types of must allow the following conclusions: • the membranes used for study’ sake enable an excellent retention of must components; • the wine so obtained are very close to those produced by bleeding and chaptalization, white wine excepted because RO concentration of must slightly rise their acidity; • the preparation of red wine musts is essential for good operation of RO; • the specificity of the product and the strengths relative to the membrane fouling lead us to define as optimum operating conditions: maximum pressure value of about 75.105 Pa , temperature between 10 and 15°C and maximum reduction volume factor that corresponds to AP equal to 15°.