Respiration quotient and yeast metabolism

Authors give an extended explanation and a simple mathematical model of the change of respiration quotient (RQ) during carbohydrate based baker's yeast propagation. On the basis of stoichiometric equations and applying the concept of the equivalents of available electrons, useful and simple expressions were deduced on the relationship of RQ to the overall cell yield. It is a widespread misunderstanding that the higher the C-incorporation is the lower the RQ will be. On the contrary, the direction of change and the value of RQ depend not only on the C-incorporation (composition of cells) but on the substrate composition as well. In conclusion, it is shown that RQ is a very informative fermentation variable but to use it as a control parameter is not as easy as usually thought.