A novel heat-flux calorimeter was used to study the aerobic batch growth of the facultative yeast K. fragilis on glucose [50-99-7], galactose [59-23-4], lactose [63-42-3], and deproteinized whey permeate. The calorimetric data enabled optimization of the defined medium compn. with respect to vitamin and trace element requirements. Direct relationship between heat evolved and biomass concn., O2 consumption rate, and CO2 evolution rate were obsd. with values for YQ/X, YQ/O, and YQ/C of 9.43, 440, and 474 kJ/mol, resp., for growth on whey permeate. The value for YQ/X varied as a function of substrate with a value of 9.43-10.59 kJ/g during growth on lactose compared with 12.66-12.82 kJ/g for growth on glucose and galactose. Energy and C balances agreed to within a few percent, esp. when alc. prodn. and stripping into the gas phase was taken into account. Using combined energy and C balances, the extent of product (EtOH [64-17-5]) formation could be estd. based on the measured biomass (YX/S) and heat yield (YQ/X). Using measured heat yields in conjunction with further exptl. detd. yields, such as the CO2 yield, makes it possible to improve the ests. of all yield coeffs. Heat measurements may constitute a valuable tool for online detns. of the concn. of biomass, O2 uptake, CO2 evolution, and product formation in a fermn. system, thereby suggesting a future for calorimetry in process design and control. [on SciFinder (R)]