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Old 04-08-2011, 04:54 PM   #1
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Default ester production. at what stage?

hi there,
i've read quite a bit on this and haven't really found a definitive answer.
at what stage of the primary fermentation are esters produced?

Let me go ahead and tell you my situation so you better understand.
i have my primary sitting in a tub (plastic tote) of water to better control my ferm temp (my ambient temp climbs to 22-23 during the day because i'm in an apartment). i have been fermenting an ale now at an even 17C for 6 days. i want to transfer to secondary and use the tub of water for my next brew which means my secondary will now be at room temp.
will i produce the majority of esters during secondary? or has that stage passed? should i hold off on my next brew and place my carboy in the tub?

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Old 04-08-2011, 05:20 PM   #2
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Quick answer: Temperature control is most important during active fermentation. I wouldn't let it get wildly out of control after that, but a few degrees won't make as significant of an impact.

Long answer: Here's a quote from Briggs 2004 (p. 462):

Originally Posted by Briggs2004
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.
The production of esters isn't terribly well understood, but the notion that it is inversely proportionate to lipid production suggests that stressed yeast will produce esters. If your yeast is already largely dormant, you are probably okay.
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