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The Big D in Only One Brand

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  • The Big D in Only One Brand

    Hey all,

    Not sure if this is the right place for this thread, but here goes:

    I have spent the last few months trying to figure out why one of my brands is having trouble cleaning itself up at the end of fermentation.

    Here is the grist:

    Avangard Munich Light (60%)
    Muntons Maris Otter (22%)
    Briess Cara 20L (8%)
    Briess Caramunich 60L (2%)
    Flaked Rye (7%)

    FW addition of CTZ. Kettle & WP additions of Comet & Cascade. Nothing outrageous as far as volume in the hop bill.

    Fermentis S-05 American Ale Yeast (500g brick in a 7 BBL batch, Original Gravity 1.060/14.7 Plato)

    Fermentation (which is standard with all of my S-05 brands): Pitch at 70.0 degF, let ferment out for ~96.0 hrs or until about 80 or 90% to TG, raise jackets to 75.0 degF until passes forced VDK test.

    Dicetyl is clearly present in this brand when a forced VDK Precursor Test is done at the start of the rest and is mildly present at the end of the Diactyl Rest (after 5 days now at ~75.0 degF) so I can tell that the yeast are starting to clean themselves up and then just simply stall before the job is done.

    I realize that the Munich Light percentage of the grist might seem high, but the malt is lightly kilned enough to be self-converting at even 100% of bill. I checked the grist's ability to self-convert even with the high Crystal & Rye and the numbers seem more than high enough to not be an/the issue.

    At first, I thought that perhaps it was just a one-off issue, but it has now happen two batches in a row to only this brand, so I am thinking it might have something to do with recipe formation rather than process. This beer is not only the only beer I have made that is between 13 and 20 SRM, but is also the only beer I have that contains Flaked Rye. Hoping that either of those things might be a red flag to someone.

    It should also be noted that there was no issue until a few months ago with this brand and I have several other brands that are of similar (& even slight higher gravity) and pitch rate (w/ S-05) that are very pale or very dark that have never had any issue with Diacetyl not cleaning itself up.

    I guess my question is:

    Does anyone see any reason that this brand might be misbehaving? Is there a reason that an Amber/Copper colored beer might have issues with the big D when paler and darker beers are not?

    Any and all advice greatly appreciated.

  • #2
    Dirty draft line?

    Are you seeing the same diacetyl character if you serve the problem brand from a different tap? Or if you pour a different brand from the tap you've normally got the problem brand on?


    • #3
      Definitely not draught lines as the issue is Diacetyl being present in Forced VDK test before the beer even leaves the primary.


      • #4
        Aeration rates?

        You might consider increasing your aeration rates a touch for this particular brand. That should help give the yeast a little extra boost to finish out secondary and diacetyl rest effectively.

        If you only recently started having problems with this brand, check all your process temperatures (mash, strike, etc.) and see if anything has changed recently, and maybe consider dropping your diacetyl rest temp by a couple degrees so as not to "over-revv" the remaining yeast in suspension.

        As a trouble-shooting procedure, if you are knocking out this brand into the same FV over and over, try a different FV. It might be an equipment issue.

        Also, if you harvest the yeast and pitch it into a different brand and still have the same problem, it might indicate a problem with the yeast itself. A different strain may be more appropriate to the beer style.

        I hope that helps. Good luck!



        • #5
          Diacetyl reductase (enzyme present in yeast) will change the diacetyl into acetoin and eventually 2,3 butanediol but it requires contact between the yeast and the diacetyl. If your yeast drops out of suspension too quickly (typical of some English strains), you will loose contact and stop the reduction. You shouldn't need to raise from 70 to 75 in order to reduce the diacetyl as this is well within the range for the yeast.

          In the first phase of fermentation, yeast will produce a lot of precursor (alpha aceto-lactate) and won't begin to clean up acetoin and diacetyl until later. If the yeast is missing Valine (nutrient deficient), it will try to create its own and produce a lot more Alpha Aceto-Lactate in the process. This can later convert to diacetyl, causing elevated levels. Check aeration levels, as mentioned, but also consider yeast nutrient additions if you do not already. It seems likely that your yeast may be doing this. If you are lacking oxygen, the cells may not be as healthy or viable as they should be. Can you run a viability and cell count on your beer? A low cell count could point to a problem with contact, and a low viability could point to a problem with the yeast metabolizing the diacetyl. Could be indicative of low oxygen or nutrient levels.

          You could try rousing the yeast late to induce more contact. You can try a form of Krausening with some fresh active wort to help finish clean up. Of course you can consider other strains that may produce less Alpha Aceto-Lactate, or ones that stay in suspension longer as another alternative as well.


          • #6
            Thanks very much for the advice!

            How big of a "yeast starter" at high krausen should I pitch into a 7BBL batch to have a meaningful impact?


            • #7
              Amber colored beers, being typically sweeter or having some of the caramel character can augment the perception of diacetyl. Another thing to look at is your nutrient levels. Do you use a yeast nutrient? If you dont, you should. Its possible that your other beers have diacetyl in them but you dont notice it due to the other flavors masking it. Might be worth sending some out for testing with a GC to tell you exactly what your VDK is between the problem batch and the others. If the yeast just quit working, you could krausen the beer with wort from another active fermentation, it doesnt take much but the yeast are very active and should clean things up.


              • #8
                Using wort/yeast from another active fermenation is a great idea!

                Thanks very much!