Composting of organic wastes saves environmental resources and helps to recover valuable constituents for agricultural purposes. Composting is a large scale bioprocess, which inherently is operated unisothermally for reasons of large scale and high oxidative metabolic activity. The autothermal pattern of internal heat generation affects the microbiology during the process. In this paper we demonstrate the impact of calorimetric approaches to composting in the laboratory and deduced implications for large scale installations, where oxygen supply, mass balances and heat dissipation calls for a thorough understanding. A comprehensive characterization of a lab-scale composting reactor was performed and the results and methodology transferred to the plant scale. Using these tools we estimated oxycaloric, coefficients and mass to enthalpy ratios. Calorimetry provided a robust and reliable tool to study the bulk-kinetics of composting.