Author Topic: Does longer fermentation = longer diacetyl rest?  (Read 2129 times)

Offline yso191

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Does longer fermentation = longer diacetyl rest?
« on: November 28, 2012, 12:17:16 PM »
One week ago today I brewed a Belgian Imperial IPA.  My target was a 1.080 OG, but overshot that and it turned out to be 1.088. The high krausen was volcanic.  There is still co2 activity in the airlock.

My plan was to do 2 weeks in the primary, then keg and let it sit at 70* for another week before cold crashing it.  But since the fermentation is taking so long, I am wondering if I need more time in the primary or warm keg before cold conditioning.

Steve

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #1 on: November 28, 2012, 12:27:57 PM »
I would think you would want to do you d-rest in the presence of as much yeast as possible as it is the yeast that are fetting rid of the diacetyl for you. It can't hurt to leave it another week at ~70f but do you taste diacetyl in the beer? what temp did you ferment at?
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Offline yso191

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #2 on: November 28, 2012, 12:33:03 PM »
 The main fermentation was done at 68*.  I used the Wyeast Ardennes which is good up to 76*, so when the fermentation slowed, I bumped the temperature 2* per day (1 AM, 1 PM), until I reached 74*. Where it has been since Sunday eve.  I have not tasted it, nor taken a gravity - I was waiting until signs of fermentation stopped.

Steve
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Re: Does longer fermentation = longer diacetyl rest?
« Reply #3 on: November 28, 2012, 12:34:38 PM »
I don't think you need to worry about a d-rest then. If you taste it and it is buttery, worry then but for now I would RDWHAHB as the saying is.
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Offline yso191

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #4 on: November 28, 2012, 12:38:24 PM »
Thank you
Steve

Offline davidgzach

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #5 on: November 28, 2012, 01:01:14 PM »
OK, I'm confused.  Why perform a diacetyl rest on an ale already at 74F?  I'm missing something.

Dave
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Offline yso191

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #6 on: November 28, 2012, 01:09:37 PM »
My understanding is that the diacetyl rest (and acetaldehyde too), is not a function necessarily of temperature, though that helps, but of time after primary fermentation.  When the yeast have used up all the sugar they can process then they begin processing the off-flavor bi-products of fermentation.

I just want to make sure that is all done before I cold condition the beer.

Steve
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Re: Does longer fermentation = longer diacetyl rest?
« Reply #7 on: November 28, 2012, 01:27:16 PM »
As I understand it acetaldehyde is a little different. The yeast aren't cleaning that up so much as it is evaporating out of the beer at temps above 70 as that is the boiling point of acetaldehyde.

with diacetyl it has to do with time and yeast activity. if the yeast have been very active the whole time they mostly clean up the diacetyl as they go. with a low temp ferment the yeast have a harder time cleaning up as they go so you raise the temp to get them more active at the end.
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Offline davidgzach

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #8 on: November 28, 2012, 02:25:42 PM »
Right Mort.  And diacetyl is much more acceptable in a Belgian IPA than in say a German Pilsner.  I would call that "cleaning up" more than a diacetyl rest which is what threw me off. 

Either way you want to say it, the advice is sound.  Leave it in primary for a week after FG to allow the yeast to clean up.  And in looking back at the thread, I would take a gravity reading and not rely on waiting for signs of fermentation to stop.  With that amount of yeast, it could let off CO2 for weeks after reaching FG.

Dave
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Does longer fermentation = longer diacetyl rest?
« Reply #9 on: November 28, 2012, 02:49:45 PM »
The main fermentation was done at 68*.  I used the Wyeast Ardennes which is good up to 76*, so when the fermentation slowed, I bumped the temperature 2* per day (1 AM, 1 PM), until I reached 74*. Where it has been since Sunday eve.  I have not tasted it, nor taken a gravity - I was waiting until signs of fermentation stopped.

Steve

Ya know, saying it's good up to 76 isn't real accurate.  IMO, the temp ranges given by yeast cos.are way too high.  Experience has shown me that I get better results at the lowest end of their range.
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Offline davidgzach

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #10 on: November 28, 2012, 03:15:37 PM »
Yea, good thing he started at 68F because with the "volcanic" fermentation, it was probably hovering around 76F as it was!

Dave
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Offline yso191

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #11 on: November 28, 2012, 03:21:58 PM »
Yea, good thing he started at 68F because with the "volcanic" fermentation, it was probably hovering around 76F as it was!

Dave

No, I have a Thermowell sitting in the middle of the fermenting wort.  That is what controls the temperature.  I hop doing it the way I did, I won't get too many fusels going.

Steve
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Offline yso191

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #12 on: November 28, 2012, 03:24:22 PM »
With that amount of yeast, it could let off CO2 for weeks after reaching FG.

Dave

That I did not know.  Thank you, I'll check it when I get home.

Steve
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Offline davidgzach

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #13 on: November 28, 2012, 03:29:27 PM »
Yea, good thing he started at 68F because with the "volcanic" fermentation, it was probably hovering around 76F as it was!

Dave

No, I have a Thermowell sitting in the middle of the fermenting wort.  That is what controls the temperature.  I hop doing it the way I did, I won't get too many fusels going.

Steve

Excellent.  That makes a huge difference!  Sounds like you will have a great brew.
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Offline hoser

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Re: Does longer fermentation = longer diacetyl rest?
« Reply #14 on: November 28, 2012, 03:32:31 PM »
My question is why would you need a diacetyl rest for a Belgian strain?  In my experience diacetyl is common in lager and English yeasts, but I have never encountered it in Belgian yeasts. Acetaldehyde, yes, if removed from the yeast to soon before it finishes fermentation and cleans up by-products.  Also, pitching at that high of a temp would more likely produce acetaldehyde vs. diacetyl.

FWIW, I rarely do a D-rest.  Even on lagers.  I you pitch an appropriate amount of yeast and ferment on the cold end of the ferment temp, the yeast will eventually clean up the diacetyl and other by-products of fermentation.
« Last Edit: November 28, 2012, 05:23:36 PM by hoser »