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Thread: Diacetyl in unfiltered beer

  1. #1
    Join Date
    Oct 2003
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    Diacetyl in unfiltered beer

    The last couple of times I have brewed my unfiltered Oatmeal Stout I have detected diacetyl after it has been on tap for a few weeks. Thankfully the customers dont seem to notice and in fact are asking me to brew it again, but I dont want to brew it again until Im sure diacetyl won't show up. THe fermentations go fine, and the beer is diacetyl free at the time of tapping...I even noticed trace amounts at the tail end of a fruit beer batch. I do not have this problem with any other beer and I don't want to start filtering my stout and lose the body of the beer.
    Has anyone had a similar problem? Any info will be greatly appreciated....

    Cheers!
    Pete

  2. #2
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    Sep 2005
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    I'd guess that your beer lines have yeast in them which are fermenting the beer in the lines after a while. Maybe a real good cleaning and sanitizing of the lines would clear it up.
    Last edited by Woolsocks; 12-09-2005 at 10:08 AM.

  3. #3
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    A couple of things to look at:

    Yes, dirty tap lines can cause this so be sure your cleaning regiment is correct and timely. How long are you resting the beer after primary fermentation? How many generations are you running your yeast? Are you possibly harvesting early floc? Hows your oxygen input into the wort, is it sufficient? Is oxygen getting into the beer after fermentation?

    If the diacetyl isn't there and then creeps up later, I would suspect that you are not fully converting the AAL into diacetyl and then this occurs later downstream over time. Ensure at least a 48 hour VDK rest, ensure the health and vitality of your yeast and procedure for harvesting, verify your o2 saturation if possible. Also make sure you are purging tanks and lines and keeping o2 out of the beer downstream because this combination with AAL with continue the pathway resulting in diacetyl in "packaged" product. The bottom line: create the diacetyl quickly and reduce it quickly and thoroughly.

    Hopefully this help,
    Good luck!
    -Beaux

  4. #4
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    The draft lines are cleaned every two weeks and I push sanitizer everytime a beer is transferred in to the serving vessel, and everytime a keg is taken offline for an extended period of time and it is unlikely that O2 is getting into the beer post fermentation.
    Beaux-what to you mean by VDK rest?

    Thanks a lot for the input guys...

    Pete

  5. #5
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    VDK= Vicinal DiKetones (includes diacetyl)

    VDK rest is also called the diacetyl rest by many brewers (same thing), since diacetyl is the major (VDK) compound being converted by the yeast.

    How long are you resting the beer after primary fermentation?

    -Beaux

  6. #6
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    Beaux -

    Typically I will cap my fermeters towards the end of fermentation, and will let the beer continue to ferment at 20 - 22 degrees C until fermentation has ceased (when pressure stops building) then chill to 13 - 15 degrees C for about 2 to 3 days then crash to 1 - 3 degrees C and apply head pressure(if below 10psi) until the day of tapping. I have never done a diacetyl rest as this problem is recent and rare, but should I be raising the temp after chilling the beer?


    Pete

  7. #7
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    Hastings, MI, USA
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    I've seen different temps quoted for a VDK rest, from 11C up to 15.5C -- personally I do mine at 12.7C for 48 hours. A test I learned is to take a sample from the zwikel, and gradually (and indirectly) heat it to around 32-33C, as it hits that temperature, smell it. If you detect the butter-butterscotchy aroma, you need to rest it longer. What works for me might not work for you, but I find making sure that the diacetyl reduction process is done completely ensures that it doesn't show up later down the line.

    Good luck!
    "By man's sweat and God's love, beer came into the world" -- St. Arnold of Metz

  8. #8
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    Does the heat accelerate the conversion of AAL to Diacetyl?

  9. #9
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    Warmer rest temperatures (usually at or near fermentation temp) accelerates the conversion. I believe the test that Rob is using is to volatize what "D" might be in the beer masked by the cold temperature.
    -Beaux

  10. #10
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    London, United Kingdom
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    hi,

    i have seen this in tap beer, the most likely cause (i think) is lactic acid bacteria from dirty lines or taps. two weeks is not that frequent for cleaning, i would suggest that it should be a weekly routine.

    cheers,

    alex

  11. #11
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    Every week would be ideal if you are pushing unfiltered product. Are you using any finings? If so, then two weeks should be ok (from experience). I would suggest an experiment to see if this is truly the issue. Compare a sample from your lines, then compare a sample taken directly from the keg/serving tank. Does the problem point to lines or the beer itself. When you are cleaning lines, are you pulling apart the faucets also? This is often an overlooked source of line flavor problems. Also, how old are the lines and have they always been well cared for?

    Let us know how it turns out!
    -Beaux

  12. #12
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    West Chester, PA
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    What yeast are you using? is it healthy? how old is it (generations). Floc and VDK production are both early occouring problems in mutated yeast. Also, VDK reduction is strain dependant....ringwood is bad, and so are most early droppers. Also, easy draft line check: if you get D at the tap, go take some out of the zwickle....if you have it at the faucet, but not at the tank then it is bacterial in the lines. otherwise its fermentation / o2 related.

    cheers

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