2.5.3. Heat production
In order to obtain optimal yields, fermentations must be carried out at constant temperature. We now discuss the parameters affecting the heat balance of a fermentation process.
The rate of heat production due to stirring, gassing/aeration and due to the metabolic activity of the microorganisms must be balanced by the heat loss resulting from evaporation and radiation plus heat removal by the cooling system.
During metabolism, heat evolution is a consequence of the thermodynamics of the overall microbial activity. Apart from anaerobic digestion and some other thermophilic microbial activity, the amount of heat produced is usually so high that if it is not removed it raises the temperature of the contents of the fermentor to a level beyond the optimum range for the system.
The evolution of heat during metabolic activity is related to the utilization of the carbon
and the energy source. When the carbon source is being actively incorporated into
biomass trough anabolism during growth, about 40-50 % of the available enthalpy in the
substrate is conserved in the biomass, the rest being given off as heat. When the carbon
source is being