Fermentation : A BioMi 290/291 MicroWeb Movie Page
Glycolysis (via the traditional Embden-Meyerhoff pathway) is the enzymatic breakdown of glucose into pyruvate. This process requires ADP and NAD+ as co-factors , and produces ATP and NADH inside the cell. A cell can always find a way to hydrolyze ATP back into ADP when needed (no oxidation/reduction is involved in ATP hydrolysis), but NAD+ is a more difficult problem, as its formation involves oxidation of NADH. Under aerobic conditions, the electrons from NADH can ultimately be passed to oxygen, but under anaerobic conditions, another electron acceptor is needed.
The following animation shows how one kind of fermenting cell re-oxidizes its NADH. You should be able to recognize the major steps in Embden-Meyerhoff glycolysis.