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I've been using a fridge w/thermostat to control fermentation temperature for ~6 months now & have recently started dual-purposing the fridge for a keg as well. Since serving & fermentation temperatures don't match I can't run them both in the same fridge simultaneously.

In order to maximise beer drinking time, I'd like to aim to regulate fermentation temperatures for the shortest time possible. At what part of the fermentation process (or any other process really) is temperature control most valuable? The first hours while yeast gains a foothold? Conditioning? The whole lot? How much ambient temperature fluctuation do I really need to care about?

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3 Answers

In terms of controlling esters/fusels/flavors, my understanding is that temperature control is most important in the first 48-72 hours of fermentation. But in terms of yeast happiness, temp control can be more important for a longer stretch.

If the temperature of the beer will rise after you turn off temp control, then you don't have a big problem. But if the temperature will drop, then you'll probably want to keep the temp control on for longer. Once the temp drops, some yeast (especially English strains) will simply stop working, leaving you with a green, unfinished beer.

Since my basement is so cold, I tend to keep temp control on for 7-10 days, warming the beer at the end to encourage diacetyl cleanup.

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This applies to ales, but not really lagers. –  mdma Feb 17 '12 at 11:50
    
Good point. I haven't made a lager, so if someone else wants to answer this question with a focus on lagers, that'd be great. –  Hopwise Feb 17 '12 at 13:51
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For lagers, temperature control is critical for the first week or two. Some lager yeasts have a fairly narrow band of fermentation temperatures ca. 10 degrees F/5 degrees C - going too high will produce a fruity lager, too low can stall the ferment, so the temperature controller is needed to help fix the temperature and avoid swings that will negatively affect the beer.

A diacetyl rest is needed by most lager strains after primary - storing the beer for 24-48 hours at 62-68 F facilitates this (depending on yeast strain.) After that, cold lagering for several weeks, between 34F/1C and 43F/6C is typical.

The temperature of the the diacetyl rest and lagering is less critical than primary ferment, so you can avoid using the temperature controller if you have an area where you can put the fermententor that is at a suitable temperature.

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I find that controlling temperature is most vital when the fermentation begins to slow down.

If you start your temperature on the low end and allow it to rise naturally, that works well until the yeast stop fermenting so vigorously.

When fermentation slows, the heat starts to drop. When the heat starts to drop, the yeast start to go to sleep. This can be bad if they aren't done cleaning everything up, so I try to make sure the temperature doesn't ever drop until at least a week into fermentation (generally a few days beyond the point that fermentation started to slow).

That is an oversimplification. In general, "the entire time it's fermenting" is the best time to temperature control and you'd be better off serving at a different temperature than wrecking your fermenting beer by accident.

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