Quantitative calorimetry has been developed in a production scale bioreactor with a volume of 100 m(3), using continuous and dynamic methods that require a heat balance be developed around the bioreactor. In order to measure the components of heat balance accurately, the precise measurements of all temperatures and flows were installed in the bioreactor. The on-line measurements of these terms then permitted the on-line calculation of metabolic heat flux from general energy balance in Eq. (1). Good correlation was obtained between oxygen uptake (OUR) and metabolic heat production rates both in continuous and dynamic methods. The metabolic heat production was also estimated from heats of combustion of substrate, biomass and ethanol and compared with experimentally measured values and good correlation was obtained. Biomass concentration was estimated from elemental, electron and heat balances and reasonable estimation have been performed using heat balance calorimetry. Direct relation has been found between cooling water flow rate and metabolic heat flux that simplifies monitoring microbial activity in large-scale fermentations. Dynamic method also allowed quick and practical estimation of overall heat transfer coefficient in the heat exchanger and reduction in the coefficient due to fouling on the surfaces of the plates could easily be identified. The results of this study suggest that quantitative calorimetry in a production scale bioreactor can be simplified by accurately identifying individual heat sources and can be realised using simple instrumentation as compared to the sensors currently used in industry. (C) 2004 Elsevier B.V. All rights reserved.