Diacetyl and Dry Hopping

[pfgonzo]

I am having a problem with my IPAs. Every batch I dry hop seems to develop an off-flavor about a week after the dry hop addition. I've been meaning to take a bottle to my LHBS to see what they think the flavor is (diacetyl or some oxidation issue). I don't know that I would call it buttery/popcorn, but it's close. It seems more like toffee to me, but I fully admit my sniffer isn't the most refined. Anyway, it does not effect my non-dry hopped beers (pales, blondes, ambers, and porters)

I have a single tier 3-burner setup. Once in the fermenter and hit with the 02 wand, I have a temp controlled fridge where I typically keep my IPAs at 66-68 or so (depending on my mood) for 4 days before allowing the temp to rise to 70-72. US-05 by the way.

I keep it there until a total of 2 weeks has elapsed since active fermentation. After that, I chill the fermenter for a couple of days (35ish) to ensure most of the solids drop out.

I then rack to my keg, make the hop addition and pressurize to 12psi. Stays chill till I'm ready to serve. My first pull, about a week in with low carbonation at that point, tastes pretty good, but after 2 weeks or so, the off flavor appears in spades. It's not as detectable while there is a head on the pint, but once the head fades the hop aroma masking the off flavor/smell is reduced and it comes out strongly.

I googled the issue, and found this thread on Probrewer: http://discussions.probrewer.com/showthread.php?34257-Diacetyl-from-Dry-Hopping

No real answers there, and was curious if anyone here had any thoughts, or a similar experience.

This has happened with cascade, amarillo, and crystal so far. I should disclose that my dry hop source is typically from a sealed package that I opened for the brew day two weeks prior. I fold over the package, tape it shut, and throw it back in the freezer till dry hop time.

Thanks!

 

[duboman]

Diacetyl is definitely butter popcorn and will leave a slick feeling along your teeth, like slimy/slick. Oxidation would be like wet cardboard, maybe sherry like in some cases, both being pretty easy to detect.

I suppose it's possible it's from dry hopping but I do a lot of dry hopping and have never had any of those issues. I too store my hops in the freezer but I use zip-loc bags once opened and purge the air out. I suppose if your hops weren't fresh or kept properly they can produce off flavors as it's been reported by others. My experience with old stale hops is like smelling old wet sneakers, nasty, nasty!

Not sure about toffee......

The other issue you raise is when this problem appears after a couple weeks in the keg, this could mean you are developing an infection once its packaged. When was the last time you thoroughly cleaned and sanitized your set up meaning lines, taps, everything? Diacetyl is usually pretty quick, oxidation a little longer to develop.

 

[pfgonzo]

I pull my first taste after about a week on the gas, and my second a week later. It's the second pint where I notice the issue. Kegs are PBW soaked and Star San rinsed each brew. Lines/taps get a cleaner flush and star san soak every two.

I popped off the keg lid and peeped inside recently. No pellicle or obvious sign of infection.

I'll bottle up one this weekend and take it to MoreBeer (3 miles away.. woo!), and see what they think it is. I wouldn't describe the taste as cardboard or sneaker, but what do I know

 

[user 70770]

I don't think diacetyl can comes from hops. It's metabolized by yeast from organic compounds in the malt. So I suspect the faults you're tasting are either present in the beer prior to dry hopping, and are simply not detectable when the beer is very fresh. Or the off-flavor is something else. I've heard that some hops can give a bit of a soapy character. I think that could be described as being slick, a bit like butter. I don't know specifically about the varieties you described however.

Also, pH can substantially affect the malt character. What does your water look like?

 

[VikingChrisColby]

Diacetyl can come from a variety of sources. One of these is oxygen being introduced into the beer late in fermentation (any time after high kräusen, really). The oxygen stimulates the yeast and they give off diacetyl (as they do in early fermentation), but then they don't take it all back up because they flocculate at the end of fermentation or are otherwise separated from the beer.
Oxygen can get introduced when you dry hop with whole hops as air is trapped between the bractioles in the cones. One way you can minimize this is to purge the whole hops with CO2 before dry hopping. If you dry hop in a keg, drop a pellet of dry ice in the empty keg, then place the bag of hops on top of it. Lay the lid on the keg loosely. After the dry ice sublimates, rack the beer into the keg. The CO2 from the dry ice will have displaced most of the air entrained in the hops.

http://beerandwinejournal.com/dry-hops-n-dry-ice/


Chris Colby
Editor
beerandwinejournal.com

 

[pfgonzo]

Chris (I'm a Chris too), one thing I don't do is purge a keg before racking. Nor do I add the dry hops before I rack. I've been adding them on top once the beer is in the keg.

I do pressurize and purge after the keg is filled, but I will make those changes and see what happens.

 

[duboman]

Chris (I'm a Chris too), one thing I don't do is purge a keg before racking. Nor do I add the dry hops before I rack. I've been adding them on top once the beer is in the keg.

I do pressurize and purge after the keg is filled, but I will make those changes and see what happens.

Neither do I and I use whole cone in the primary as a dry hop frequently, I don't think it's that.

I find it odd that it's appearing late after packaging and nothing prior and that's a couple weeks time from FG.


Sent from the Commune

 

[user 70770]

I'm not convinced the oxygen trapped in the hops are the problem. First off, the beer is allowed to ferment for 2 weeks and is most likely fully attenuated by then. Second, the beer is crashed cooled and kept cool which should stop any latent yeast activity during dry hoping. I think the problem is either hop derived compounds that give the appearance of diacetyl, or it's a water chemistry problem.


Sent from my iPhone using Home Brew

 

[JaimeTheLimey]

Sounds like you're doing all the right things and I suspect it's diacetyl conversion. I've been having the same problem for some time and think I've finally figured it out.
Alpha acetolactate is the precursor to diacetyl which is a byproduct of fermentation and common in finished beer. The problem is that once you introduce 02 it converts to diacetyl. If you have enough AAL in your finished product, it's inevitably going to convert once you introduce 02 (i.e. transferring, dry hopping, etc.)

Commonly you fight it by making sure your yeast is happy (i.e. oxygenating, high pitch rates, etc.) None of this has helped me yet. I just can't get the yeast to clean up the beer.

Last batch of IPA I did was tested after primary for diacetyl and was definitely positive. I threw the carboy on a stir plate very low just to keep the yeast in suspension. After about 36 hours the diacetyl was almost undetectable. Another idea (which I'm going to try on my next batch) is to hit it with a little 02 when it's half way to FG. This, in theory, should force the AA to convert to diacetyl, thus giving the yeast more time to clean it up.

I've also shot an email to White Labs to see if they have any suggestions. Seems to me that the yeast is just too efficient and dropping out before it has a chance to clean up. I'll post back if/when I hear from them.

Here's a good article on diacetyl. Try doing a test next time before you transfer from primary. That will tell you if excessive AAL is present and hopefully alleviate some head scratching. Good luck!
http://www.professorbeer.com/articles/diacetyl.html

 

[pfgonzo]

Interesting. My last couple non-IPA beers were big and I "roused" the yeast after the first week to keep things going. I wonder if you're right and the strains are just too flocculent. I'll try rousing on my next IPA as well. Eventually something will work and I'll have to back off on each to figure out which!

 

[pfgonzo]

Update: Had the awesome people at MoreBeer taste it, and the consensus is I am crazy. No diacetyl and no oxidization. The aroma/flavor I am detecting is from the CaraRed I added to my last couple of IPAs for color. It apparently imparts a strong malt aroma/flavor (which I interpreted as toffee), and I didn't make the connection!

Live and learn!