[mpietropaoli]

-TLDR version of the questions:  How long could/should you keep fermented beer on the yeast at 72 degrees after reaching an appropriate final gravity before racking/bottling to minimize off-flavor compounds (I’m particularly gunshy about diacetyl and acetaldehyde)?
 
-Does biere de garde benefit from cold-crashing, and if so, can I cold crash on the yeast, or do I need to rack to a carboy?
 
 
I brewed a 55 gallon batch of biere de garde with my homebrew club this past Saturday.  We came out a little light on FG (1.061, compared to recipe target of 1.067), and also had an issue with our plate/pre-chiller set up, and only got most of the wort down to the mid-70’s/low-80’s.  We split up the wort (each guy got 5 gallons).  I had to leave early, and the guy who hosted pitched a cup of Brewer’s Art Resurrection (dubbel) yeast at about 75 degrees, and kept it in his basement, ambient temp of about 70.  Came back a day later, fermenter temp was about 75 with vigorous airlock activity.  Took my fermenter and another for a fellow member and put them in my ferm chest, and dialed back the temperature.  Per Jamil’s recipe, I set the controller to 66 degrees, and placed the probe on the outside of my fermenter (ale pail) with styrofoam/tape on the outside to insulate it from the ambient temp inside the ferm chest.
 
Jamil says to raise the fermentation temp by one degree or so per day once fermentation slows until you are at 72.  As I noticed airlock activity slowing (I didn’t take a gravity reading) two nights ago, I let it creep up to 67, then 68 last night.  I plan to take a gravity reading tonight.  Also, in Chris White’s book, he notes that a great technique achieve proper attenuation is to pitch on the warmer side (mid/high-70’s), let fermentation start, then ratchet it back to your desired temp (as we did here, somewhat accidentally).  The only caveat is that if you do this, you need to raise the temp back up at the end of fermentation to clean up these compounds.
 
Here are my questions: I have been operating under the wisdom that as homebrewers, we should not take beer off the yeast for at least 2 weeks.  Even if the krausen subsides and FG is reached, leaving the beer on the yeast can ONLY benefit the beer (autolysis seems to be less of a concern with today’s yeast strains).  However, I am new to temp control, and I know commercial brewers regularly have primary fermentations in the 6-7 day range.  Also, I would like to cold crash this for at least a month.  Should I take it off the yeast before doing so?
 
thanks in advance!

[nateo]

I rarely like to ferment any yeast over 64* or so. I usually aim lower on all styles. I really hate noticeable fusels, but some people like and/or expect them in certain styles, so YMMV.

Ale yeast produces and then cleans up diacetyl and acetaldehyde very quickly, so you don't really need to worry about those unless your ferment is done in like 2 days.

Go ahead and cold crash if you want improved clarity. All the Biere de Gardes I've seen were pretty hazy, so I don't think cold crashing is crucial.