The macro- and micromixing properties of a continuous flow Taylor-vortex reactor can be optimised by changing the conventional cylindrical rotor geometry into a novel ribbed one. A chemical test reaction, the micromixing-sensitive alkaline saponification of ethylacetate with separately fed reactants, was used to probe the mixing performance down to the molecular level. Experiments were performed in a continuous flow Taylor-vortex reactor equipped either with a conventional cylindrical rotor or with a novel ribbed rotor in a wide hydrodynamic range of 150 < Ta < 8000 and 0.8 < Re < 2.0. Through increase in the reaction temperature and the feed concentrations, the relaxation times of this reaction were reduced from 680 to 19s and compared to micromixing times by monitoring the reactor conversion. The results show that a TVR with conventional rotor achieves intense micromixing at high rotor speed, but behaves like a CSTR. In contrast, a device with ribbed rotor shows macromixing features close to those of a plug flow reactor (PFR) in a wide range of rotor speeds: however, segregation of the two feeds could only be dissipated at slow reaction rates, i.e. relaxation times larger than 64s. (C) 2009 Elsevier Ltd. All rights reserved.