The incubation process of binary mixtures of vinasse and grape mare was studied to optimize the rate of each component for composting purposes. Mixtures with increasing amounts of vinasse (0-40%) were incubated in a laboratory scale reactor under aerobic conditions at 55 degreesC for 43 days. Changes in pH did not show great differences among the mixtures. The organic matter (OM) evolution shows higher losses and higher values of biodegradability in mixtures with lower amounts of vinasse. The losses of Kjeldahl-N increased when the amounts of vinasse in the mixtures increased, A kinetic study based on the model of Whang and Meenaghan showed that the calculated values of 1/K-1 (an index of the stability of the substrate-microorganism complex), increases with increase in the vinasse ratio in the mixtures, The available nutrients supplied by the vinasse favored microbial growth. However, a decrease in the values of K-2 (values that depend on the operational parameters of composting process) was observed when the vinasse ratio was increased in mixtures probably due to the increase in salinity and decrease of pH in the mixtures that limit microbial activity. The addition of vinasse simultaneously affects the incubation process both positively and negatively, and hence, moderate amounts of vinasse (between 10 and 20%) would be the best compromise. (C) 2002 Elsevier Science Ltd. All rights reserved.