Torrefaction tests were carried out in a thermobalance and in a lab-scale device on beechwood and on its constituents e cellulose, lignin and xylan. The main volatile species measured were water, formaldehyde, acetic acid and carbon dioxide. Thanks to measurement before volatiles condensation, the yield of formaldehyde was shown to be higher than usually observed in literature. Smaller amounts of methanol, carbon monoxide, formic acid and furfural were also quantified. Each constituent did not produce all species. Beech torrefaction could be described by the summative contribution of its three constituents up to 250 _C. At 280 _C and 300 _C, tests performed with constituents mixtures showed that there were interactions between cellulose and the two other constituents. A hypothetical mechanism was proposed to explain these interactions.