The reasons for the increase in the rate and enantiomeric excess after oxidative (aerobic) treatment of Pt/alumina in ethanol have been investigated. It is demonstrated that their treatment results in the formation of acetic acid and consequently in the protonation of the quinuclidine N1 of cinchonidine. This favours the cinchonidine-pyruvate interaction and improves enantioselectivity. In addition, the reaction rate is enhanced due to acid catalysis of the carbonyl. reduction. NMR and UV measurements indicate the rapid transformation of ethyl pyruvate to the corresponding hemiketal in primary alcohols as solvents. It is shown that the possible involvement of this hemiketal (and that formed between cinchonidine and ethyl pyruvate) as an intermediate in the pyruvate hydrogenation mechanism can be excluded.