A central composition design was developed to study the influence of process variables (temperature, pulping time and ethanol concentration) on the properties of the pulp produced (yield and holocellulose, alpha -cellulose and lignin contents) and the pH of the resulting wastewater, in the ethanol pulping of olive tree trimmings. The proposed equations reproduce the experimental results for the dependent variables with errors less than 5% for the holocellulose and alpha -cellulose contents, yield and wastewater pH, and less than 15% for the lignin content. Obtaining pulp with acceptably high yield (37.6%), high holocellulose and alpha -cellulose contents (above 88.8% and 46.9%, respectively), and low lignin contents (below 7.2%), entails operating at a pulping temperature of 200 degreesC, using an ethanol concentration of 75% and a pulping time of 60 min. (C) 2001 Elsevier Science Ltd. All rights reserved.