A comparative study of two pressing processes for white wine production was carried out using membrane presses. In one of them, the vintage was pressed after crushing and destemming and in the other a maceration process in the wine press itself. In this way, significant differences were established between the press fractions and between the two pressing systems used. Quantification of individual phenolic compounds was carried out by high performance liquid chromatography. Compared with direct pressing, maceration process increased the levels of phenolics in the must, including those with physiological properties. A greater yield of free run must was obtained by strategic use of skin contact maceration. (C) 2003 Elsevier Ltd. All rights reserved.