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Old 05-18-2011, 02:12 PM   #1
ayoungrad
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Default Diacetyl Test and Diacetyl Rest Length

I have my first lager (a 1.065 Pilsner) in the fermenter. It got down to 1.014-1.017 at one week, so I rasied the temp to 65 (from 52) for a diacetyl rest.

After 2 days at 65, I pulled a sample last night to recheck gravity and to do a diacetyl test. The gravity was 1.009 and the krausen had fallen.

For the test I put one half the sample in the frig. I heated the other half to 140 for about 30 minutes (intending to heat for 60 minutes). Then I read somewhere that a covered sample at 160 for 10-20 minutes was better, so I increased the temp and kept it covered with aluminum foil during the 10 minute heating.

There was no hint of butter in the cooled sample. There was horrible buttery aroma in the heated sample. Great... diacetyl.

So, last night I agitated the fermenter and increased the temp to 68 and I'm planning to retest tommorow night.

Is there anything else I can do? (I do not have krausen available.)

Also, does the diacetyl test detect ANY diacetyl or only that which will be noticeable in the final product? The smell was so in your face that I'm just concerned it will never completely go away.

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Old 05-18-2011, 02:39 PM   #2
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The smell was so in your face that I'm just concerned it will never completely go away.
Its not going to go away on its own. I have done 5 lagers this year already and 4 of them had diacetyl after fermentation and lagering regardless of pitching temps, the only beer that did not had diacetyl is the one I pitched on a cake from previous batch. But don't worry. If you keg, I suggest to make small batch of beer about 1.5 quarts (1.040) and pitch in keg at high krausen just as it starts fermenting. Newly started fermentation will scrub any diacetyl as result. After week or so, chill beer down to 32F or lower to drop yeast out of suspension. I fixed all of my beers this way. It works so good that in fact I will do this for all my lagers in future, 1.5 qt starter will also carbonate your beer to about 2 volumes of CO2 so you killing to birds at same time.
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Old 05-18-2011, 02:40 PM   #3
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Its not going to go away on its own. I have done 5 lagers this year already and 4 of them had diacetyl after fermentation and lagering regardless of pitching temps, the only beer that did not had diacetyl is the one I pitched on a cake from previous batch. But don't worry. If you keg, I suggest to make small batch of beer about 1.5 quarts (1.040) and pitch in keg at high krausen just as it starts fermenting. Newly started fermentation will scrub any diacetyl as result. I fixed all of my beers this way.
So, in your opinion, a diacetyl rest does not work at all?
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Old 05-18-2011, 02:49 PM   #4
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So, in your opinion, a diacetyl rest does not work at all?
from my experience - not really. I tried everything. I waited till fermentation was down to 1.025-1.020 (75%) and then move fermentor to room temp - diacetyl. I tried wait out till fermentation completely over than move it to room temp - diacetyl. Note that I always pitch cool (50F) so I think the problem is stressed out yeast or starters not big enough in first place.
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Old 05-18-2011, 02:54 PM   #5
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Interesting. I pitched a little warm at 58 degrees. I used Saflager 34/70 so I didn't use a starter but I pitched 3 rehydrated packs and aerated with oxygen for a little over a minute.

So, stressed yeast shouldn't be the issue but I suppose you never know.

I do not keg, so while I suppose I could try a small batch and pitch it into the ferementer I'm not really psyched about it. But if I were to go this route, what do you reccommend for yeast? I would imagine something clean like US05?

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Old 05-18-2011, 03:01 PM   #6
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Interesting. I pitched a little warm at 58 degrees. I used Saflager 34/70 so I didn't use a starter but I pitched 3 rehydrated packs and aerated with oxygen for a little over a minute.

So, stressed yeast shouldn't be the issue but I suppose you never know.

I do not keg, so while I suppose I could try a small batch and pitch it into the ferementer I'm not really psyched about it. But if I were to go this route, what do you reccommend for yeast? I would imagine something clean like US05?
For small beer I used some W34/70 I had laying around. If you bottle, your diacetyl might be scrubbed up in the bottle by the yeast when they will chew on your priming sugar but I don't know for sure
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Old 05-18-2011, 03:52 PM   #7
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How long have you extended your diacetyl rest in the past?

I'm trying to avoid a starter beer addition for several reasons. But I'm also surprised that some people feel a rest doesn't work when it is all over this site and is discussed in "Yeast".

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Old 05-18-2011, 05:21 PM   #8
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How long have you extended your diacetyl rest in the past?

I'm trying to avoid a starter beer addition for several reasons. But I'm also surprised that some people feel a rest doesn't work when it is all over this site and is discussed in "Yeast".
I had beer sitting for up to a week at room temp for diacetyl rest, most suggest 48 hours but it takes about 24 hours just to warm up to room temperature. I've read most, if not all on diacetyl rest on this forum as well, but as you probably experienced for yourself its not always work the way others describe. There is just too many variables between batches, yeast, brewers, equipment, techniques etc. I think I gained the most valuable info about diacetyl from this article: Diacetyl: Formation, Reduction, and Control
Hope this helps to understand it a little more.
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Old 05-18-2011, 05:31 PM   #9
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If the yeast need sugar to clean up the diacetyl, why not add a few ounces of corn sugar to the fermenter when doing the diacetyl rest? The amount used to bottle prime isn't supposed to change the flavor or the ABV.

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Old 05-18-2011, 05:32 PM   #10
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I'm trying to avoid a starter beer addition for several reasons.
"starter beer" addition called krausening (do a search on that) and it might be your only solution if you don't want to dump a batch. Germans used this technique to carbonate their beer since priming sugar was not allowed due to 1516 purity law. I naturally carbonate my kegs of lager this way, addition of krausening beer not only cleans up diacetyl but also carbonates my keg within week or two.
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