How long is temp important?

If I ferment a typical Ale, how long is it important to keep it in the desired temp range?

Here is an example: I am brewing an American Wheat using Rogue Pacman. I got it down to between 60-66 and can keep it there with water/ice bath.

Is it important to keep it in that range only for 4-5 days? Or should I really strive to keep it at that temp for 2 weeks (how long I usually leave in primary).

What is the chemical process that makes the temperature important? I understand the yeast will throw flavors at high temp, but couldn't they be doing that during secondary/keg/bottling etc? It seems like there would be a huge dropoff in temperature importance once the bulk of the sugar is gone, but I don't really understand the processes that continue to happen with the yeast after most sugar is gone. I understand that the yeast "clean up the beer" but I don't really know what that means and if it is temperature sensitive.

Also, what about after I keg it? Can it sit there at 75 for 3 weeks?

From my experience, once active fermentation is over the ester production drops to a point where it is not noticeable. It does not stop completely but once I am done with active fermentation I rack to a secondary to make room for my next brew. After that the secondary or kegs can be stored at reasonable temperatures without any impact that my unrefined palate can detect. Though if your down south and it's 110F outside I would not store them in the garage.

Anyone else have an opinion here? Rather than define "active fermentation" can I just have a rule like "keep it cool for 5 days" ?? Yes I know I'm being lazy. I want to take temp seriously, but I can only cool 1 batch at a time and its a bit of a pain so I'm trying to tighten up the timing.

I've been wondering the same thing lately. I want to make room in my ferment fridge but don't want to jeapordize a batch by moving it to room temp too early. I have racked to a secondary to put in a room temp closet before, but haven't been doing that lately and my beers have been better. However, I think that's due to my brewing improving and not the room temp secondary.

I pulled a tripel out of my 68* fermenter yesterday after 2.5 weeks to rack to secondary and free up space, and before I even got the lid off the bucket, it started bubbling away again (like a bubble every 7 seconds) so I put it back in the fridge.

Once high krausen has been reached and the krausen starts to fall, the risk of the yeast producing flavor-active compounds above taste threshold greatly diminishes, even if the temperature is raised. Once fermentation reaches the 75% complete mark, the risk is virtually nil. In fact, yeast will attenuate better (perhaps not noticeable in SG reading) and clean up some of the compounds produced earlier in fermentation with a raised temperature near the end of fermentation (like a diacetyl rest).

Maintaining cooler temps in most ales beyond fermentation (within reason) is unnecessary (to a point). However, yeast cells will decay (not necessarily autolysis) faster at higher temps and, in doing so, could produce noticeable off-flavors in cleaner beers if left on the primary yeast/trub for extended periods at higher temps.

menschmaschine said:

Once high krausen has been reached and the krausen starts to fall, the risk of the yeast producing flavor-active compounds above taste threshold greatly diminishes, even if the temperature is raised. Once fermentation reaches the 75% complete mark, the risk is virtually nil. In fact, yeast will attenuate better (perhaps not noticeable in SG reading) and clean up some of the compounds produced earlier in fermentation with a raised temperature near the end of fermentation (like a diacetyl rest).

Maintaining cooler temps in most ales beyond fermentation (within reason) is unnecessary (to a point). However, yeast cells will decay (not necessarily autolysis) faster at higher temps and, in doing so, could produce noticeable off-flavors in cleaner beers if left on the primary yeast/trub for extended periods at higher temps.

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Ok thanks! This is great info. The beer I started on Saturday still has a thick krausen on it but is has shrunk a bit. I know this is not how it works, but would you say a rule of like one week at temp is enough? Ideally, I'd do less than a week, but I know fermentation time varies yeast to yeast. With Notthingham, for example, it seems like 3 days and it's usually done with most of fermentation, so maybe I can stop chilling then.

At this point, in my garage, not chilling the beer it is in the 70-78 range. So that is what I would let it hang at after the first fermentation period. I'm not looking for an easy way out - I want to get this temp control down tight and optimize my process.

Picobrew said:

I know this is not how it works, but would you say a rule of like one week at temp is enough? Ideally, I'd do less than a week, but I know fermentation time varies yeast to yeast.

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You answered your own question there. It depends on too many factors to put a rule-of-thumb timing on it. Each fermentation is going to be different and it's best to wait near the end of fermentation before raising the temp. If that's 3 days, great... if it's two weeks (maybe on a big ale fermented in the lower end of the optimum range), you're better off waiting.

menschmaschine said:

Once high krausen has been reached and the krausen starts to fall, the risk of the yeast producing flavor-active compounds above taste threshold greatly diminishes, even if the temperature is raised. Once fermentation reaches the 75% complete mark, the risk is virtually nil. In fact, yeast will attenuate better (perhaps not noticeable in SG reading) and clean up some of the compounds produced earlier in fermentation with a raised temperature near the end of fermentation (like a diacetyl rest).

Maintaining cooler temps in most ales beyond fermentation (within reason) is unnecessary (to a point). However, yeast cells will decay (not necessarily autolysis) faster at higher temps and, in doing so, could produce noticeable off-flavors in cleaner beers if left on the primary yeast/trub for extended periods at higher temps.

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From experience I would agree with everything here. However being the science forum and all does anyone have a study or source of some sort to cite confirming this? I'd love to read it... and have something to cite later should I need to... other than Chapter 12.10 in Brew science, which btw has quite a bit to say on the topic. But you might need to take a entry level Biochem class to understand if you don't pick up on context really well.

FWIW, my SOP is to let keep ales cool during the active fermentation which is usually just 3-4 days...then I just let the whole thing (carboy in water bath) warm up to room temp for the remainder. I keep it inside (in A/C), my garage is too warm during most of the year and can have fairly big temp swings (I would avoid large-ish temp swings). My ales are generally pretty clean, I actually sometimes struggle getting enough esters. Even doing this with Weizen/Belgian yeasts doesn't yield very much banana (phenols yes, banana no).

In fact, yeast will attenuate better (perhaps not noticeable in SG reading) and clean up some of the compounds produced earlier in fermentation with a raised temperature near the end of fermentation (like a diacetyl rest).

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This is the main reason I tried doing it this way...I thought it might actually be better. I can't say I've noticed any difference but I wasn't getting off flavors before either (it's very possible I can't detect diacetyl though). But it's certainly easier this way.

This is a good thread, and I have wondered the same thing myself. My tentative logic is congruent with that of menschmaschine.

I usually ferment at 66-68 F for about a week. By that time most fermentations are about done, so to make room I move them to room temp (78-80) during the summer. Results have been good. I do treat wheats and Belgians differently.

Greenbird - How do you treat your wheat beers?

I'm no authority on the subject, but I like to ferment them at about 70 - 72 F to get a good ester profile, then drink them fast, because they're best when drank young.

Thanks. I am a little closer to 75 with mine - my wife decided my poor boy cold box was asthetically unpleasing and ordered its removal from the house, so I have no acceptable means to chill it without dropping it to kegerator temps.
I am certainly looking to get this in the keg quick as my Belgian Gold looks like it will blow tonight and will be back on store bought.

Provided you are using a suitable hefe yeast, I would be comfortable with 75 as long as I employed the wet t-shirt trick, since the yeast might cause your temp to get up above 80 during full krausen without it. That would keep it in the low to mid 70's, which should be good.

You've said you want tight control, but also mentioned the lazy factor Totally understandable, but this is the part of the process you really have to be careful of.

For tight control, which you want, you can't afford to be lazy and go with set times. You must be able to see the fermenting wort, so buckets suck for this. Use clear carboys, and check the beer every day. The bulk of potential off-flavors are produced during the lag and growth phases of the yeast. Let them grow cool (right under your main fermentation temp if possible) and allow them to raise the temp to your main fermentation target if they want, and hold them there until they start to tire. Watch for the krausen to start falling back into the beer. At this point the yeast is getting tired and have already done most of their fermentation work. Give them a shot of energy by raising the temp at this point, and they will eagerly finish up their work and start cleaning house. From here, I wait until the beer starts to actually clear up. The krausen should totally disappear, and the liquid should gain lots of clarity. This means you can soon cold-crash to put them all to bed.

Different yeast strains do these things in hugely different time frames. Don't ever trust a set time schedule, even if you know EXACTLY what to expect from a strain. Things happen and you have to go by what the yeast wants, you can listen to them but you can't tell them what to do

Cheers and GL! Remember don't set and forget!