Ethyl valerate (green apple flavour) and hexyl acetate (pear flavour) are short-chain esters with fruity notes that are widely used in food, cosmetic and pharmaceutical industries. Crude Staphylococcus simulans lipase was immobilized on different supports. The CaCO3 was selected as the most suitable support offering maximum adsorption capacity. Different reaction parameters for enhancing ester formation were investigated. In fact, higher conversion of ethyl valerate (51%) was achieved by the addition of 20% (w/w) of water to the reaction mixture, using 200 IU of immobilized lipase, a molar ratio valeric acid to ethanol of 1 and at 37 degrees C. No decrease of the synthesis activity was observed for 10 cycles of use of the immobilized lipase. In the case of the hexyl acetate, the optimum conditions, giving 41% of conversion, are obtained with 10% (w/w) of initially added water, 100 IU of immobilized lipase, a molar ratio acetic acid to hexanol of I and at 37 degrees C. Immobilized lipase could be repeatedly used for five cycles without a decrease of synthesis activity. (c) 2006 Elsevier Ltd. All rights reserved.