ester production. at what stage?

Briggs2004 said:

The synthesis of esters requires the expenditure of metabolic energy suggesting that ester formation must fulfil an important metabolic role. It may be a mechanism for regulating the ratio of acyl-CoA to free CoA (Thurston et al., 1981). Peak ester concentrations are reached after the formation of higher alcohols has ceased (Fig. 12.1). Rates of ester synthesis are maximal at the mid-point of fermentation coinciding with the cessation of lipid synthesis. Thus, when acetyl-CoA cannot be utilized by lipid synthesis, the formation of esters provides an alternative use for this substrate. Intermediates of lipid biosynthesis influence ester formation. Supplementation of worts with the unsaturated fatty acid, linoleic acid (50 mgl􏰀1) causes a dramatic decrease in ester formation (Thurston et al., 1982). It was suggested that this effect was due to inhibition of alcohol acyl- transferase by unsaturated fatty acids. This effect has been confirmed by others (Yoshioka and Hashimoto, 1982a, b, 1984) and led to the proposal that ester and lipid syntheses are inversely correlated. This is supported by the observation that increasing oxygen supply to wort tends to decrease ester synthesis. In this case, oxygen promotes the synthesis of unsaturated fatty acids, which in turn reduces the activity of alcohol acyltransferase.

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