So once again, under anaerobic conditions, glycolysis still occurs, which means that we break down glucose into two pyruvate molecules and produce a net of two ATP molecules. In the process, we also deplete our pool, our concentration of NAD plus molecules. But we need these NAD plus molecules for glycolysis to continually take place. So that implies that we must have some way to regenerate the NAD plus molecules by oxidizing NADH back to NAD plus. And since under anaerobic conditions, the NADH molecules do not actually go onto the electron transport chain, another method of regenerating the NAD plus molecules is via the process of fermentation. And there are two types of fermentation processes.