By means of a microcalorimeter (direct calorimetry) and a Warburg-apparatus (indirect calorimetry) that part of the dissipation of a growing culture of yeast cells which remains irreversible in the cells is determined (psi u). The course of the psi u-function with time correlates with the increase of the specific cell concentration being conditioned by the growth phase of the culture but similar for fermentative and respirative metabolism.

The heat evolution of aerobic batch cultures of growing yeast (Saccharomyces cerevisiae) in glucose media was investigated by a combination of a flow-microcalorimeter with a fermentor vessel. The course of heat production, cell production and the rate of oxygen consumption were qualitatively the same for all glucose concentrations between 10 mM and 100 mM. Under optimal aerobic conditions a triphasic growth was observed due to the fermentation of glucose to ethanol, respiration of ethanol to CO2 and acetate, and respiration of acetate to CO2. Energy and carbon were found to be in balance for all glucose concentrations.

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