When the conversion of pyruvate → acetaldehyde → ethanol is blocked in yeast, the NADH generated in glycolysis must still be reoxidised. S. cerevisiae achieves this by diverting dihydroxyacetone phosphate → glycerol, using glycerol-3-phosphate dehydrogenase. This is exploited industrially with bisulfite addition (which traps acetaldehyde) to direct fermentation toward glycerol production.