the unique economic pressures of wartime sometimes provide in-centive for scientific discovery. Two examples from the First WorldWar involve the production of organic solvents by the microbial fermentation of readily available carbohydrates,such as starch or molasses. The German side needed glycerol to make nitroglycerin. At onetime the Germans had imported their glycerol,but such imports were prevented by the British naval blockade. The German scientist Carl Neu-berg knew that trace levels of glycerol were usually produced during thealcoholic fermentation of sugar by Saccharomyces cerevisiae.He sought to develop a modified fermentation in which the yeasts would produce glycerol instead of ethanol. Normally acetaldehyde is reduced to ethanolby NADH and alcohol dehydrogenase (figure 9.10,pathway 2). Neubergfound that this reaction could be prevented by the addition of 3.5%sodium sulfite at pH 7.0. The bisulfite ions reacted with acetaldehyde andmade it unavailable for reduction to ethanol. Because the yeast cells stillhad to regenerate their NADϩeven though acetaldehyde was no longeravailable,Neuberg suspected that they would simply increase the rate ofglycerol synthesis. Glycerol is normally produced by the reduction of di-hydroxyacetone phosphate (a glycolytic intermediate) to glycerol phos-phate with NADH,followed by the hydrolysis of glycerol phosphate toglycerol. Neuberg’s hunch was correct,and German breweries were con-verted to glycerol manufacture by his procedure,eventually producing1,000 tons of glycerol per month. Glycerol production by S. cerevisiaewas not economically competitive under peacetime conditions and wasended. Today glycerol is produced microbially by the halophilic algaDunaliella salina,in which high concentrations of intracellular glycerolaccumulate to counterbalance the osmotic pressure from the high level