Heavy Diacetyl in Stout

Hello all,

I brewed an AG stout in May of this year, and throughout fermentation and bulk aging it tasted fantastic. The recipe was for the most part the Kate the Great clone found on this site. I aged in on French oak for 2 months, and then bottle conditioned in late August. I consumed the first bottles in September, and they tasted good though a bit undercarbed. I have noticed though that bottles I open now have a very heavy nasty popcorn butter flavor and aroma- so much so that when I smell the beer it seems more like Chardonnay than stout.

So, any ideas on what caused this? The fermentation was NOT temp controlled, so the temperature could have easily climbed into the 70's. S-05 was used. This does not seem to be the culprit though as the beer was bulk aged for well over a month at the same temps, which should have taken care of any residual diacetyl. Also, the flavor was not detectable in bulk aged samples.
I have heard that excessive oxidation can cause diacetyl production- while my bottling was not out of the ordinary in any way I can think of, I'm thinking this was the point of introduction. If this is the case, can I realistically expect the diacetyl to age off? Should I cellar the stout for a year or two in hopes that it will turn into something great, or should I just trash it now and save myself the trouble?

Thanks to anyone who has some input!

I recall reading somewhere that although we always assume diacetyl only occurs as a biproduct of fermentation, it can also result from bacterial infection. In this case that seems like the more likely culprit. Introducing something like oak into the equation could be a possible source if it wasn't handled very carefully--and even then you never know.

osagedr said:

I recall reading somewhere that although we always assume diacetyl only occurs as a biproduct of fermentation, it can also result from bacterial infection. In this case that seems like the more likely culprit. Introducing something like oak into the equation could be a possible source if it wasn't handled very carefully--and even then you never know.

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I'll second that. Did you sterilize the oak before adding it to the secondary? Cheers!!!

osagedr said:

I recall reading somewhere that although we always assume diacetyl only occurs as a biproduct of fermentation, it can also result from bacterial infection. In this case that seems like the more likely culprit. Introducing something like oak into the equation could be a possible source if it wasn't handled very carefully--and even then you never know.

Click to expand...

Indeed - diacetyl is a byproduct of Pediococcus fermentation.

Yeah, I have read the same thing that pedio can cause diacetyl as well, but I really have a hard time thinking this is the cause. The oak was handled very carefully- I received a French oak stave from Maker's Mark that was fresh out of a barrel, then it was chipped into smaller pieces and resoaked in fresh Maker's for well over a month...it seems like this should have killed any bugs on or in the oak.

Second, I have had a beer get a pedio/lacto infection before and it showed many symptoms that this one isn't- overcarbing, thinning of body, heavy bandaid aroma, sour/acidic flavors and overall funkiness. This beer isn't showing any of those- the malt profile is very nice, and the carb level is still on the low side of proper for the style. It's just this damn buttery slickness on top of it all. I'm just hoping to hear any similar stories to see if people have had success aging this flaw out.

Thanks for the replies!