Theoretically, the yield is 0.511 for ethanol and 0.489 for CO2 on a mass basis of glucose metabolized. Two ATPs produced in the glycolysis are used to drive the biosynthesis of yeast cells which involves a variety of energy-requiring bioreactions.
Therefore, ethanol production is tightly coupled with yeast cell growth, which means yeast must be produced as a co-product.
Without the continuous consumption of ATPs by the growth of yeast cells, the glycolytic metabolism of glucose will be interrupted immediately, because of the intracellular accumulation of ATP, which inhibits phosphofructokinase (PFK), one of the most important regulation enzymes in the glycolysis.