diacetyl reduction with time?

[JayDubWill]

I brewed an Oktoberfest lager and ended up with a diacetyl bomb. I was originally going to dump the keg but being inherently lazy I didn't get around to it until today, 3 months and a day since I brewed it and probably two months since I tasted it. It's been hanging out in my kegerator at ~44F degrees. I decided to give it one last taste before I did the deed and was surprised that I tasted significantly less diacetyl than I had previously. It's still present but where before I couldn't even finish a pint, It was almost pleasant to drink now. I was under the impression that once your beer developed diacetyl there was no way to reduce it. Is it possible that this extended lagering has reduced the diacetyl level? Should I take it out of the fridge and let it sit at room temp another month or two to speed up the process? Has anyone else experienced a diacetyl bomb that turned out drinkable given enough time?

 

[staph_mcgee]

Yeast will re-metabolize diacetyl. A warmer temperature where the yeast are more active will affect the time it takes. "Diacetyl rest" is a fairly common practice in commercial brewing to my knowledge, although ideally it's to reach ideal flavor profile, not to reach something just drinkable. I'm not sure if there is a limit to what the yeast can re-metabolize.

 

[bobeer]

I have the same issue with my Oktoberfest as the OP. When it's cold right out of the fridge it's easier to drink but once it warms up it becomes a bit harsh with a diacetyl taste. I'm going to let it age out and see if it helps. Thanks for the input!

 

[biertourist]

If you guys are using the Weihenstephaner lager strain, it's FAMOUS for being super slow to ferment and super slow to take up diacetyl. (Well technically it's just slow to do anything.) -I have the same issues when using it but it makes such a DELICIOUSLY malty beer I used it for my Oktoberfests and Bocks anyway.

Diacetyl does not "age out"; it can ONLY be reduced by the active work of yeast on the converted diacetyl so if you tranfer off of the yeast you're going to have problem reducing the diacetyl. (Yes, I'm being pedantic here but "age out" usually refers to off flavor reduction as a simple function of time and when talking about diacetyl it's important to note that without the presence of plenty of healthy yeast, it just won't be reduced.)


What you should do is a "Diacetyl rest" (for up to 2 weeks at elevated temps); the diacetyl rest does 2 things: 1 it converts the diacetyl pre-cursors to diacetyl sooner so that it can actually be reduced (this happens much faster at warmer temps), 2 it increases the metabolic rate of the yeast so that they take up diacetyl faster.

I also recommend "krausening" your beer with fresh actively fermenting beer- simply take some of the yeast from your fermenter and make a "starter" after primary fermentation then at high krausen pitch it back into the fermenter (which should now be at diacetyl rest temps).

Most yeast strains actually can take up and convert the same quantity of diacetyl; the "diacetyl prone" strains simply are more likely to produce more diacetyl on the front-end.


In the future you can pitch MORE yeast, add a diacetyl preventing additive at pitching (can't remember the name right now), make sure that you only pitch yeast to COLD wort (no lager tradition pitches warm), and/or use a less diacetyl prone lager strain.

Some brewers far wiser than me have quipped the phrase that "Diacetyl is just an indicator of an impatient brewer." Keep the beer on that yeast and just wait it out; lager brewing is a slow, slow process.



Adam

 

[ajdelange]

...add a diacetyl preventing additive at pitching (can't remember the name right now)

It is called Maturex made by Novozymes (who are kindly sponsoring the free WiFi connection for attendees at the MBAA conference in progress in Austin as I write).


If you kegged your beer with a goodly amount of yeast in suspension then they will reabsorb diacetyl. If you did not then there is no mechanism by which diacetyl can be reduced and I would have to ask 'Are you sure it is diacetly'. I well remember being given a beer to taste which the brewer (a good one) had told me was a 'diacetly bomb', the very term you used. I had no perceptible diacetyl. I there was any its flavor and aroma were completely masked by acetaldehyde. It was an 'acetaldehyde bomb'. Not saying that is the case here but even good brewers get mixed up some times.

 

[JayDubWill]

good information from all, thank you. Diacetyl as a sign of impatience is probably the truest thing I've heard all month. I did a d-rest on this Oktoberfest on day 5 of primary for 4 days. I raise the temp 10 degrees higher than what I ferment at, in this case I raised it to 60F. I probably should have done the diacetyl test where you heat the beer up but I never had a problem with it before. Looking at my notes I used 5th generation Wyeast 2206 Bavarian Lager. As far as it possibly being acetaldehyde, I wasn't tasting any green apple but was getting a strong buttery flavor and slippery mouthfeel. The more I brew and learn about lagers the more respect I have for anyone who can do them well.

 

[ajdelange]

That certainly sounds like diacetyl. Unless there are active (even if only slightly active) yeast cells in the beer I cannot think of any mechanism which would convert diacetyl to acetoin or butanediol. Even Maturex doesn't touch diacetyl - it converts the alpha aceto-lactate directly to acetoin. Maybe, given enough time, something in the beer, if it is in reduced state, will reduce the diacetyl but I can't imagine that happening in a time period as short as suggested by OP.

 

[dannysk]

Diacetyl will certainly be reduced by yeast over time. Of course, it is a function of yeast strain, yeast health, temperature, pH and oxygen levels (the later two since diacetyl reduction (and increases) can also happen non-enzymatically as a redox reaction). I do think, however, that 44 dF is too low and at that temp the reactions will still take place but it will be at a very slow rate. Allowing the lagering temp to increase will help the diacetyl reduce since (I believe) that temperature is the most important factor in diacetyl reaction in any given fermentation/lagering. If your yeast are rather flocculent and have settled, that will also work against you.

Just make sure that the diacetyl is not going up because if that is the case, it is due to a bacteria infection. Most likely a pediococcus sp. and that can not be fixed.