Regulation mechanism of ester formation by dissolved carbon dioxide during beer fermentation.

Shantha Kumara, H.M.C., Fukui, N., Kojima, K. and Nakatani, K.

Abstract
Acetate esters in beer, including ethyl acetate and isoamyl acetate, are formed by the yeast during fermentation. The reaction, catalysed by the enzyme alcohol acetyltransferase (AATase), synthesizes esters from the corresponding alcohols and acetyl CoA, and can be inhibited by a number of factors. While it has already been shown that the suppression of this reaction by certain unsaturated fatty acids, lipids and sterols is due to inhibition of enzymic activity, the nature of the mechanism of its suppression by excessive levels of dissolved carbon dioxide in the fermenting wort has hitherto remained unclear. Experiments are described in which it was shown that higher carbon dioxide levels have no effect on AATase activity but do lead to a decrease in the acetyl CoA content of the yeast cells, indicating that the mechanism in this case probably involves the suppression of acetyl CoA synthesis, perhaps by inhibiting the activity of one or more of the enzymes concerned (probably pyruvate decarboxylase).
Keywords : brewers' yeast carbon dioxide ester inhibition production