Author Topic: What exactly is a diacetyl rest and  (Read 7090 times)

Offline Wildrover

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What exactly is a diacetyl rest and
« on: December 07, 2008, 06:10:44 PM »
how do I do one?

Thanks

Offline MaltLicker

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Re: What exactly is a diacetyl rest and
« Reply #1 on: December 08, 2008, 07:04:07 AM »
Diacetyl is a compound generated by the yeast in most beers, and its level or concentration varies by yeast strain and beer style.  Most styles should not have any, but a handful of styles allow for a tiny amount.  (People's sensitivity to diacetyl varies wildly, so "tiny amount" is subjective.)

Most yeast strains will usually "clean up" the diacetyl if given sufficient time in primary to complete the job.  So leaving the beer on the primary yeast cake thru the entire fermentation cycle is key.  Additionally, if your yeast strain or beer style recommends a diacetyl rest,  it means raising the ferm temp 2 or 3 degrees Fahrenheit towards the end of the active ferm, often in the five to eight day range. 

At that stage, the yeast is tired, drunk, and finishing off the more complex sugars and also trying to clean up diacetyl and other typical by-products of the fermentation.  Raising the temp slightly helps the yeast with the clean up.  Raising the temp may also keep the yeast eating and achieve 1-2 more points of attenuation. 

Offline UselessBrewing

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Re: What exactly is a diacetyl rest and
« Reply #2 on: December 08, 2008, 07:19:01 AM »
+1
Mostly on Lager Yeast's.

Cheers
Preston
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Offline Wildrover

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Re: What exactly is a diacetyl rest and
« Reply #3 on: December 08, 2008, 09:44:02 AM »
So is this an issue for ale brewers?  I'm thinking the best thing to do is to just let it sit on the yeast a day or two after primary fermentation is over?

Offline MaltLicker

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Re: What exactly is a diacetyl rest and
« Reply #4 on: December 08, 2008, 12:01:59 PM »
All yeast create it.  I think ale yeasts are quicker to clean it up than lagers.  The typical cause is racking off primary too soon.  (A friend judged an ale Saturday that wreaked of diacetyl - could not smell anything beyond the butter.) 

From WyeastLab.com  http://www.wyeastlab.com/he_b_fermentation.cfm
............Diacetyl reduction takes place during secondary fermentation and during the diacetyl rest that some brewers incorporate into the secondary stage of fermentation.

Secondary Fermentation Summary:
• Decreased rate of ethanol and CO2 production
• Diacetyl Conversion
• Reduction of some flavor compounds by yeast metabolism or CO2 scrubbing

Offline Wildrover

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Re: What exactly is a diacetyl rest and
« Reply #5 on: December 08, 2008, 03:49:37 PM »
Seems like the lesson here is patience.  As someone who brews primarily ales Im thinking my best course of action is to just let the beer sit in the primary until I'm sure its done then move to the secondary as I always do and things should take care of themselves? 

Offline UselessBrewing

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Re: What exactly is a diacetyl rest and
« Reply #6 on: December 09, 2008, 07:03:56 AM »
It wont hurt the beer to leave it for a short while. On that note, I have a friend who travels a great deal. He has an Oatmeal stout in the primary now for 3 months. I Cant wait to try it to see how it handled the extended period on the yeast. Although I fully expect it to be a great beer because it started life as a BIG beer. But it will be interesting to see.

Cheers
Preston

The woodpecker pecks, Not to annoy, But to survive!

 

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