How long for a diacetyl rest?

Discussion in 'Homebrewing' started by mikehartigan, Apr 17, 2014.

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  1. mikehartigan

    mikehartigan Maven (1,421) Apr 9, 2007 Illinois

    I brewed a Wheat beer two weeks ago using T-58 yeast. I fermented it in the garage, but the temps were quite a bit lower than I anticipated (30F-45F during most of that period). Even the day that the local temp hit 80F, the beer never got above 55F. While I fully expect the beer to be less than optimal (it is what it is), I'm most concerned about diacetyl at this point - something I can actually address. I plan to move it into the 72-ish house for a couple of days to give the yeast a chance to clean this up. Is it reasonable to plan to serve it this Sunday? How long does it take to effectively clean up diacetyl?
     
    #1 mikehartigan, Apr 17, 2014
  2. JackHorzempa

    JackHorzempa Grand Pooh-Bah (3,375) Dec 15, 2005 Pennsylvania
    Society Pooh-Bah

    Mike, according to the below write-up from an article in BYO it sounds like 2 days for the diacetyl rest. Is your beer at final gravity? I am uncertain how effective a diacetyl rest specifically is if the beer is at final gravity?

    Have you tasted your beer to confirm that is does indeed have a high level (i.e., a perceptible level) of diacetyl?

    Cheers!

    Jack

    “Give It a Rest

    It is important to provide sufficient maturation time for diacetyl reduction. This step is commonly known as a “diacetyl rest.” Diacetyl reduction is slower at coldertemperatures, so it is essential to incorporate the diacetyl rest when making cold-fermented lagers.

    The process is simply to raise the fermentation temperature from lager temperatures (50° to 55° F) to 65° to 68° F for a two-day period near the close of the fermentation. Usually the diacetyl rest is begun when the beer is two to five specific gravity points away from the target terminal gravity. The temperature is then lowered to conditioning temperature following diacetyl reduction.

    For ale production, the fermentation temperature is usually 65° to 70° F, so temperature modification is not necessary. But the fermentation should still be “rested” at this temperature for two days to ensure proper diacetyl reduction. Many brewers make the mistake of quickly crashing the fermentation temperature following terminal gravity. Why not? The beer is done, people are thirsty, and there is no taste of diacetyl in the beer.

    Even though the diacetyl can’t be tasted, however, the beer might contain high levels of the precursor, acetolactate, which can be converted to diacetyl. Once the yeast is removed, there is no way to get rid of the diacetyl.”
     
    #2 JackHorzempa, Apr 17, 2014
  3. VikeMan

    VikeMan Grand Pooh-Bah (3,067) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    I typically do about 2-3 days, at 68-ish. I do it whether I have tasted diacetyl or not, because diacetyl can still form after attenuation is finished.

    You don't *have* to start ramping up before attenuation is finished. But it's a time saver than seems to have no repercussions.
     
    #3 VikeMan, Apr 17, 2014
  4. mikehartigan

    mikehartigan Maven (1,421) Apr 9, 2007 Illinois

    I haven't taken a gravity reading, but, given the temp over the past two weeks, I would be surprised if it was done. I was thinking that if I warm it up, it'll finish up in a day or two. Cleaning up the diacetyl will happen more or less at the same time.
    As a beer drinker, I was blessed with an inability to taste diacetyl :slight_smile:. As a brewer, I was cursed with this deficiency :slight_frown:. Just trying to be sure.
     
    #4 mikehartigan, Apr 17, 2014
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  5. VikeMan

    VikeMan Grand Pooh-Bah (3,067) Jul 12, 2009 Pennsylvania
    Pooh-Bah

    It's cheap insurance, given varying taste thresholds and given the fact diacetyl could still form after you taste the sample anyway.
     
    #5 VikeMan, Apr 17, 2014
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