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Diacetyl from Dry Hopping?

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  • Diacetyl from Dry Hopping?

    I've started noticing a correlation to the beers that we dry-hop and the levels of diacetyl or diacetyl-like flavors in our final batches. We use the same yeast for a number of our brews and the ones that don't get dry hopped NEVER have this characteristic, but it is abundantly present in those that we do. We do nothing differently when it comes to diacetyl rest or any other process changes, just that the only ones with the diacetyl are the ones that we dry hop. Has anyone had any experience with this or have any advice on how to correct this? It's really pissing me off and I can't seem to grasp why this would be caused simply by the process of dry-hopping. Thanks!

  • #2
    I would guess that you are introducing oxygen in your dry hopping process which is then pushing diacetyl precursors into diacetyl. There are a number of ways to deal with this depending on what your setup actually is.

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    • #3
      At what point in the process are you dry hopping?

      What weight of hops are you adding, to how much beer?
      dick

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      • #4
        Originally posted by AnthonyB View Post
        I would guess that you are introducing oxygen in your dry hopping process which is then pushing diacetyl precursors into diacetyl. There are a number of ways to deal with this depending on what your setup actually is.
        Do you perform a forced Diacetyl test before dry hopping?

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        • #5
          Hey guys, I brew with Ben. To answer your questions about our dry hopping routine, it's pretty textbook. With the beer in question we are using WLP007 yeast and ferment at 66F. As with all of our beers, after terminal grav is reached - usually day 4-5 - I cut the glycol and let the temp rise to the upper 60's for several days of diacetyl rest. Then at day 7, I begin a slow crash, but with our dry hopped beers, I only bring it down to 60F. Then after a few days at 60 I dump whatever yeast has flocced in the cone and dry hop from the top of the fermenter, with pellets, straight from the hop bag, keeping everything as sanitary as possible. On this particular beer we do 44lbs pellets dry into 30bbl of beer. This last time I split the 44 lbs into two days, 22lbs each day. It then has about 2 days at 60F after dry hopping and then I begin a slow crash.

          I don't usually do a forced diacetyl test because we have never had a diacetyl problem and have always allowed the yeast plenty of time to clean up any precursors. The few times I have done a test, I never got any diacetyl. Keep in mind we use this yeast on several of our beers, including a light blonde, even after being used in these dry hopped beers, and never get any detectable diacetyl in any other beers, at any point. Furthermore, I don't see how we could possibly be introducing that much O2 while dry hopping into a fermenter that is full of pure CO2.

          One other strange thing we've noticed is that a few times after we have detected diacetyl in a beer after kegging, it actually diminishes after sitting in the keg for a month or two at 35F. It's been my experience that once you have diacetyl, it doesn't ever go away and usually only gets worse. Needless to say we're pretty baffled and frustrated.

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          • #6
            Diacetyl?

            It may not be diacetyl at all. Especially given the beer is diacetyl-negative after fermentation and the flavor 'goes away' after conditioning.

            I thought for the longest time that a local brewer consistently had high levels of diacetyl in one of their beers, a pale ale with loads of Galaxy hops, until I tried some other commercial examples that had the same apparent 'flaw'. I have also noticed this flavor in a heavily-hopped beer I made.

            You might be detecting a cheesy/rancid flavor given off by old/poorly stored hops, over-extraction at high temps (either with dry hops or hop debris carried over in the fermenter), or a combination thereof, and mistaking it for diacetyl. Maybe this flavor is more apparent in certain hop strains (Galaxy?) than others?

            I'm reaching a bit here, since this is all from personal experience. I'll have to dive into my books on Hops/IPA to check for supporting info.
            Kyle Kohlmorgen
            Process/Automation Consultant
            St. Louis, MO

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            • #7
              Originally posted by SouthHouseBrew View Post
              It may not be diacetyl at all. Especially given the beer is diacetyl-negative after fermentation and the flavor 'goes away' after conditioning.

              I thought for the longest time that a local brewer consistently had high levels of diacetyl in one of their beers, a pale ale with loads of Galaxy hops, until I tried some other commercial examples that had the same apparent 'flaw'. I have also noticed this flavor in a heavily-hopped beer I made.

              You might be detecting a cheesy/rancid flavor given off by old/poorly stored hops, over-extraction at high temps (either with dry hops or hop debris carried over in the fermenter), or a combination thereof, and mistaking it for diacetyl. Maybe this flavor is more apparent in certain hop strains (Galaxy?) than others?

              I'm reaching a bit here, since this is all from personal experience. I'll have to dive into my books on Hops/IPA to check for supporting info.

              We have certainly had this thought as well, and we are particularly sensitive to diacetyl here, but unless there is some other chemical that smells and tastes buttery, I don't know what it could be.

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              • #8
                I use a blend of 75% 005 and 25% 007 in my IPA. I have never had issues with diaceytl. I ferment at 72 F with a 3 day diaceytl rest crop yeast then dry hop 1 LBS per bbl for one week.

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                • #9
                  Originally posted by brewmaster 2011 View Post
                  I use a blend of 75% 005 and 25% 007 in my IPA. I have never had issues with diaceytl. I ferment at 72 F with a 3 day diaceytl rest crop yeast then dry hop 1 LBS per bbl for one week.
                  Do you leave the beer at 72 for the whole week after dry hopping?

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                  • #10
                    That is a huge dry hop rate compared to the rates used by most UK brewers at least. Nothing wrong with that as such, but this is equivalent to 8 ounces per 9 UK gallon cask. I have only ever come across as much as 2 ounces per 9 gallon cask. For that reason, I suspect you might be correct in your assumption about the diacetyl, simply due to the entrained air as you add to the vessel. If virtually all your yeast has dropped out, and you have little or no residual fermentable sugars left, then the remaining yeast is likely to produce diacetyl as a result of the oxygen addition, but with so little yeast and fermentable sugar left, the diacetyl is not converted to less pungent compounds such as acetoin, which is what normally happens in British cask beer - hence the other comment "after we have detected diacetyl in a beer after kegging, it actually diminishes after sitting in the keg for a month or two at 35F". This is one benefit of extended long maturation times - there is sufficient time even at low temperatures for the remaining yeast to mop up the diacetyl.

                    Now I'm assuming that you are getting the hops in sealed vacuum / nitrogen flushed bags, but if the bags have been opened and only partially used, there will be air/oxygen in the hops. I also assume you break the hops up from their compressed state to allow them to disperse better. It might be worth trying to flush the broken up hops through with CO2, or nitrogen if you have it and making absolutely sure that the flushed bag is only re-opened once below the CO2 level.

                    It only takes a few mls of air to introduce one ppm of oxygen which is more than enough to lead to diacetyl generation. Have you an oxygen meter you can use to check dissolved oxygen before and after (say an hour after) addition?

                    I don't discount the other comment that you might be tasting something other than diacetyl though.
                    dick

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                    • #11
                      Originally posted by dick murton View Post
                      That is a huge dry hop rate compared to the rates used by most UK brewers at least. Nothing wrong with that as such, but this is equivalent to 8 ounces per 9 UK gallon cask. I have only ever come across as much as 2 ounces per 9 gallon cask. For that reason, I suspect you might be correct in your assumption about the diacetyl, simply due to the entrained air as you add to the vessel. If virtually all your yeast has dropped out, and you have little or no residual fermentable sugars left, then the remaining yeast is likely to produce diacetyl as a result of the oxygen addition, but with so little yeast and fermentable sugar left, the diacetyl is not converted to less pungent compounds such as acetoin, which is what normally happens in British cask beer - hence the other comment "after we have detected diacetyl in a beer after kegging, it actually diminishes after sitting in the keg for a month or two at 35F". This is one benefit of extended long maturation times - there is sufficient time even at low temperatures for the remaining yeast to mop up the diacetyl.

                      Now I'm assuming that you are getting the hops in sealed vacuum / nitrogen flushed bags, but if the bags have been opened and only partially used, there will be air/oxygen in the hops. I also assume you break the hops up from their compressed state to allow them to disperse better. It might be worth trying to flush the broken up hops through with CO2, or nitrogen if you have it and making absolutely sure that the flushed bag is only re-opened once below the CO2 level.

                      It only takes a few mls of air to introduce one ppm of oxygen which is more than enough to lead to diacetyl generation. Have you an oxygen meter you can use to check dissolved oxygen before and after (say an hour after) addition?

                      I don't discount the other comment that you might be tasting something other than diacetyl though.
                      Our hop rate is definitely high for UK beers, but this is more of an American west coast pale. We just use the English ale yeast on this one because we like it and have it readily available. But we ferment is at the low temp range on this beer to prevent the fruity esters that typically come out of this yeast.

                      But back on point...basically this same dry hopping method is used by many large breweries here in the US. I like to wait until after terminal gravity because I want most of the yeast to fall out so that I can crop it and reuse it. I don't want to reuse yeast with a bunch of hops in it.

                      As far as O2 introduction...I always dry hop out of freshly opened, nitrogen-flushed bags. I do break up the pellets. Also, I usually have around a .5 psi head pressure on the tank before opening the top port, so that when I open it, CO2 is venting and theoretically no outside air could be entering. So I just can't believe that we are getting enough O2 introduction to cause the slight remaining yeast to produce precursors. And it stands to reason that if there is enough yeast to produce diacetyl, there is enough to clean it up. Maybe I'm not leaving it at 60F long enough after dry hopping. I'm certainly willing to try hopping earlier before the yeast all falls out though.

                      Unfortunately I don't have an oxygen meter to test before and after.

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                      • #12
                        Originally posted by Judd View Post
                        Maybe I'm not leaving it at 60F long enough after dry hopping.
                        That would be my guess. We dry hop the entire time at 60F; and when I talk to other brewers it seems that many (most) dry hop at this temp as well (versus cellar temp).

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                        • #13
                          Extending the warm holding time after hop addition seems a sensible way to go.

                          Re the hop addition rate - I was only pointing out that the hop addition rate is so high compared to beers I am used to that I suspected the sheer amount of hops added significant oxygen. But thinking on a little further, the trad British cask beers are stored, distributed and served warmer than I think you are cooling to, so they normally have a much longer time to mop up the diacetyl.

                          So doubling the warm storage time for instance should make a big difference.

                          But you have got me thinking about trying a beer here with similar dry hop rates. The only trouble is lack of capacity to leave in tank to mature like this as we couldn't add directly to cask for legal reasons of minimum contents, and don't have own sales outlets to try it out.
                          dick

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                          • #14
                            Originally posted by dick murton View Post
                            But you have got me thinking about trying a beer here with similar dry hop rates. The only trouble is lack of capacity to leave in tank to mature like this as we couldn't add directly to cask for legal reasons of minimum contents, and don't have own sales outlets to try it out.
                            Kind of straying off topic but have you seen the IPA Book from Mitch Steele? He goes through a number of historic UK recipes that seem excessive even by current American craft brewer standards. I attended his presentation at this year's Craft Brewers Conference and I was once again reminded how interesting some of those recipes sounded.... but then after I heard the part where the beers were cellared for 10+ months... my interest sort of waned

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                            • #15
                              Hi there,

                              Certain hop strains at certain levels can mimic diacetyl (centennials?). This is what I suspect is happening especially if you've noticed it disappear after a month or so as hop flavors and bitterness diminish over time. Diacetyl doesn't go away with time. Try a different hop and see what happens.

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