Preventing Diacetyl -or- "Hold The Butter Please" - Home Brew Forums

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Old 06-26-2008, 03:06 PM   #1
BierMuncher
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I posted this extract from another website many months ago, but thought it worth repeating. For anybody who has been dinged in a competition for detectable diacetyl levels, or those of you wanting to rush your beers out of the primary…this is a must read.

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Diacetyl is a natural by-product of fermentation. It is detectable in beer at concentrations as low as fifty parts per billion. At low levels, it gives beer a slick mouthfeel; at higher levels, the flavor becomes buttery — diacetyl is in fact what they make artificial butter out of — then like butterscotch, and eventually downright rancid. First I'll let you know where the diacetyl comes from, and then I'll tell you how to get it out of your beer.

What to do about it: You're not going to believe how simple this is. Do a “diacetyl rest”; that is, leave your beer in the fermenter for two or three days after it looks like the fermentation is complete. That's it. That will give the yeast time to clean up the diacetyl they've produced. If you're brewing an ale, the fermentation temperature is already high enough that the cleanup will proceed rather quickly. If you're brewing a lager, try this trick: start allowing the fermentation temperature to rise once the beer has fermented to half its original gravity. By that point, you're far enough into the fermentation that the yeast aren't going to generate any more “ale” characters (such as fruity esters) and you've still got enough time to let the temperature rise to a useful level, say, 65°F. Maintain this temperature until the diacetyl is gone or until the end of fermentation, whichever is later, then rack for lagering.

How can you tell if the diacetyl rest is complete? There's an easy “forcing” test that will only cost you a few ounces of beer. Pull a sample from your fermenter and split it into two covered containers. Refrigerate one and heat the other to 140°F for an hour, then taste them both. If they taste the same, you're ready to rack your beer out of the fermenter. If you can taste butter in the heated sample, your yeast is still at work, and you should give it another day or two.
Another testament to longer fermentation times equating to cleaner tasting beer.

 
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Old 06-26-2008, 03:07 PM   #2
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I keg after 3-5 weeks in primary and never notice diacetyl. The biggest thing new brewers should learn is patience...and then they should learn to never trust their airlock...
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Old 06-26-2008, 03:10 PM   #3
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Thanks for posting this BM, I have done this twice I think maybe three times after I switched up to AG. I would recommend everyone try it, just to know what to look for.
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Old 06-26-2008, 03:10 PM   #4
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So far the only lager I've made that didn't exhibit diacetyl after a 7-10 day primary is when I pitched a massive slurry at BELOW ferment temps.
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Old 06-26-2008, 03:36 PM   #5
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Do I have to raise the temps of my ales to do it? I've been getting fermentation levels in the really low 60's (like below 65) since I've been playing with harvested pacman yeast (the brewmaster of Rogue likes to ferment pacman @ 60 deg.)

Should I take it out for my chill bath for a couple days at the tail end of fermentation?
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Old 06-26-2008, 03:56 PM   #6
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Quote:
Originally Posted by Soulive View Post
The biggest thing new brewers should learn is patience...and then they should learn to never trust their airlock...
+1

I can't believe how many people think Air Lock is pronounced Hydrometer.

I understand that it's exciting having beer and all...but when your air lock stops bubbling at day #3, brew another batch and leave the first one alone. If people would leave their beer alone for 2 or 3 weeks, this would never be an issue.
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Old 06-26-2008, 04:06 PM   #7
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Great info. I always leave mine in primary two weeks before taking a hydro reading, but it's very nice to know the reasoning/science behind the method.

 
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Old 06-26-2008, 04:40 PM   #8
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Quote:
Originally Posted by Revvy View Post
...Should I take it out for my chill bath for a couple days at the tail end of fermentation?
I don't think you'd need to, but spending the last 4-5 days at a balmy 68-74 degrees couldn't hurt.

 
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Old 06-26-2008, 05:15 PM   #9
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Conversely (to play devil's advocate) I've heard experts say to take the wort off the primary as soon as possible after flocculation to avoid autolysis.

How would one balance this time? What's "too long" and what's "too short" - hypothetically speaking?
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Old 06-26-2008, 05:16 PM   #10
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Quote:
Originally Posted by cactusgarrett View Post
Conversely (to play devil's advocate) I've heard experts say to take the wort off the primary as soon as possible after flocculation to avoid autolysis.

How would one balance this time? What's "too long" and what's "too short" - hypothetically speaking?
I once left an Oatmeal Stout on the yeast for 45 days. It was one of my cleanest beers to date. Usually I never go more than 35 days though...
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