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Thread: Diacetyl from Dry Hopping?

  1. #31
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    I've had a similar problem with an IPA only once. I usually dry hop my IPA on day 7 after cropping some yeast. I will leave it then for another few days at fermentation temperature 20*C. With this particular problematic batch I tried something different by dropping the temperature of the beer to 15*C on day 7, crop the yeast on day 9 and dry hop. After kegging it was great. Two weeks later it was riddled with diacetyl. Never tried that again and I've never had that issue again.

    Now, what works for one might not work for another. I've realised there are allot of other factors contributing to a final outcome when considering different processes and techniques.

    Cheers

  2. #32
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    Quote Originally Posted by Joseph View Post
    This is a problem in big dry hopped beers. I've experienced it as a professional brewer and have tasted other breweries IPA's that had diacetyl problems that they were unaware of. So from my experience and from a friend of mine who is the Master Brewer at one of the top craft breweries in the US, have discovered that by dry hopping after the initial fermentation the hops will agitate the yeast which in turn start to ferment again and will produce VDK and diacetyl formation. I have experienced better aromatic results by dry hopping right off the bat anyway. Some hops will put off a similar aroma to diacetyl too. ----I have a theory : that with all the dry hops mixed in the fermenter with the yeast, that the hops will block some of the surface area of the yeast which in turn will not allow the yeast to fully re-absorb diacetyl during the diacetyl rest. To remedy this I added an extra day for the rest and it worked really well. Did have a problem though, when adding an extra day it was hard to not go below the intended terminal gravity. These Chico like strains do not flocculate well and want to keep going. So to troubleshoot that we did better harvesting methods to ensure genetically superior and healthy yeast; started to bung about a full plato earlier to add some extra pressure and slow the yeast down. Also just being as diligent as possible in the cellar. These IPA's are a real challenge which is why I appreciate a good one so much. ------ Cheers
    When you say dry hop right off the bat are you talking about right after yeast takes off? With yeast pitch?

  3. #33
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    Quote Originally Posted by brain medicine View Post
    When you say dry hop right off the bat are you talking about right after yeast takes off? With yeast pitch?
    These methods have proved best.

    Diacetyl in dry hopped beers, especially IPA's is a serious problem. Eliminating or reducing diacetyl and dissolved O2 (which can also bring out diacetyl) is our main goal. From my own experience and after discussing with a top brewmaster from one of the largest craft breweries in the country ~ here's what we've learned.

    ~ Risks of dry hopping towards the end of fermentation and/or during the diacetyl rest is: the stimulation of dormant yeast and yeast that are at the end of their cycle; it can start their cycle again and the end result could be: the Big D!

    ~ Another risk if dry hopping towards the end of the diacetyl rest is: hops can get in the way of (yeast's steps) of diacetyl reabsorption which in turn = the Big D!

    ~ From what I've learned about some large craft brewery techniques is to crash it, blow the yeast out and then warm it back up to 50 F and recirculate thru a hop filter of some kind. We don't have a chiller that also heats, so we dry hop as soon as the chill starts and recirc. We'll then take our time chilling bout 48 hrs and recirc again. After the fermenter hits 32 we will either filter the hops out after a couple days of crashing or blow them out (with a 20 micron filter as to not filter aroma). If recirculation is not an option or too risky, one could blow Co2 into the bottom of fermenter and stir pellets up. We only use pellets but can also filter with whole hops.

    Cheers, All ~~~~~~ Joe

  4. #34
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    I find it interesting that a lot of brewers will decide their dry hop schedule by days and not by gravity.

    Personally, I don't subscribe to the hops getting in the way of diacetyl re-adsorption theory, since I have made extremely hoppy beers without this issue. Some as much as 1kg/HL dry hop on top of .5kg/HL hot side. If there is evidence to the contrary (other than anecdotal) I would certainly be open to digesting it.

    Diacetyl and 2,3 pentanedione (VDKs) are not actually produced by yeast (if memory serves me correct). The yeast actually produces alpha-acetolactate and alpha-ketobutyrate (precursors) respectively, during the production of Valine and Isoluecine. Oxidative decarboxylation actually creates the VDKs (chemical reaction, not enzymatic reaction). Dry hopping often does rouse the yeast at least some, and that can influence continued production of the precursors. Any oxygen present at later stages offers the chance for the decarboxylation process to continue, creating VDKs later in the process.

    The VDKs can be re-adsorbed by the yeast during metabolism and converted to acetoin and butanediol, however this requires enough sugar left (and yeast health) to continue metabolizing during diacetyl rest. This is why the rest is usually performed after 2/3rds of expected attenuation but well before FG is reached. Raising temperature after FG is reached will not help reduce diacetyl significantly, and it could even possibly induce more precursor production. Timing of diacetyl rest is very important. Raising temp is not usually needed in ales, however it is still important to have the sugar left to aid in uptake of the VDKs.

    With this line of logic, I prefer to add dry hops after the majority of fermentation but before diacetyl rest. My thoughts are this avoids the aroma scrubbing that can take place under vigorous fermentation, and still allows any precursors the chance to form into VDKs prior to the diacetyl rest. Then the yeast still has a chance to metabolize and "clean up" the VDKs.

    I try not to re-pitch dry hopped yeast, however have done so many times without negative results. I don't subscribe to all the negativity surrounding this. In fact I have won medals with beers that used hopped yeast pitches. Obviously it is not "ideal", and may require higher volume/weight pitches to achieve similar cell counts. I schedule to avoid it as much as possible, but if I do need to, I try to pitch it into other hoppy beers to not taint delicate beers. I am sure there are some smarter than I who might have a differing opinion, but this has produced great results for me in multiple facilities and I am extremely sensitive to diacetyl. (So much so I don't like beers with high caramel malt even though I can taste the distinct difference between VDK and caramel malt)

  5. #35
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    A while ago I posted on this thread about me encountering diacetyl from dry hopping. Since that last post we upgraded a few things and have been experiencing VDK's from time to time in heavy dry hopped beers. What I have noticed is that the beer will reach terminal gravity on day four. We'll harvest and dry hop on day seven at 20C and recirculate the tank volume three times. Our IPA will restart fermentation and drop from 1.015 to 1.010 slowly over the coarse of 5 days.

    We have started to play around with the IPA and found that by dropping the temp down to 16C, harvest and dry hop, there was almost no change in gravity. Hopefully this could mean that no precursors where generated.

    Ill keep you people updated on our findings.

    Cheers

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