The energy-releasing metabolic process in which substrate is...

In fermentation, the incomplete oxidation of glucose is achieved under anaerobic conditions by set of reactions, where pyruvic acid is converted to $\mathrm{CO}_2$ and ethanol. The enzyme pyruvic acid, decarboxylase and alcohol dehydrogenase catalyse these reactions. In animal cells also, like muscles during exercise, where oxygen is inadequate for cellular respiration, pyruvic acid is reduced to lactic acid by lactate dehydrogenase. The reducing agent is $\mathrm{NADH}+\mathrm{H}^{+}$, which is reoxidised to $\mathrm{NAD}^{+}$, in both the processes.