Diacetyl has faded with aging

[trevorc13]

After brewing a quick Scottish 70/- (2 weeks in the carboy) for competition, I submitted it with the fear of diacetyl due to the short conditioning time. I kept tabs on the quality of the beer as it carbed and was very disappointed to find a large amount of diacetyl in the finished product. Keeping in mind that this was not yet carbed, I searched sites to see if it might clear up as it aged and conditioned. The only sites I found indicated that diacetyl only got worse with age. Luckily, my depression faded after my beer finally carbed up and the residual yeast in the bottle ate the rest of my diacetyl. This happened as I hoped and just wanted to write a quick blurb in case anyone else found diacetyl in their beer and got immediately depressed. It does fade with age if you taste it green. I believe that if it's filtered, or bottled from the keg, and diacetyl exists after conditioning time, this might not be the case, but in my situation it worked. Cheers!

 

[ajdelange]

What you experienced is exactly what should happen. Diacetyl acually forms in the package as residual alpha-acetolactate is non enzymatically oxidized to diacetyl. If active (though even at a low level) yeast are present they will reduce it to first acetoin and then 2,3 butane diol. If you package a beer with residual acetolactate (easily determined by warming a sample - the buttery odor is indicative that the stuff is present) and no active yeast then yes, the acetolactate will turn to diacetyl over time just as it does in the forced (heat applied) test.

 

[Brew_G]

I had the same experience with a couple beers I brewed with yeast j harvested from Two Hearted. I fermented in the acceptable range (my fermentation was 65-67F), but the resulting beers were serious butter bombs.

I was really upset about the first one (a slightly hoppy brown ale), as it was only my third beer, and I brewed it to serve at my daughter's birthday party. Luckily, at week three in the bottle (the day of the party), it had pretty much completely cleared up. The difference between the second and third weeks was remarkable, and at about five weeks it was a fantastic beer. For the second beer (Centennial/Columbus APA), I got tons of butter day on, but I stuck with it and hoped to have a similar result. That's exactly what happened - the butter cleared out at the third week and the beer got really good a week or two later.

I'm still confused as to how I got so much diacetyl in those beers to begin with, but I can only assume it was something to do with that yeast. I have one more beer using that same yeast - an Oberon-inspired American wheat that was fermented at 69F and is currently in the fermenter - so it'll be interesting to see what happens with it.

 

[ajdelange]

I'm still confused as to how I got so much diacetyl in those beers to begin with, but I can only assume it was something to do with that yeast.

The mechanism is explained in #2. Some yeast are faster to clean up than others, some leak more acetolactate than others and, of course, valine poor wort requires more synthesis and results in more leakage. The fact that it eventually cleaned up eliminates sarcina sickness (infection) as the cause.

 

[Brew_G]

Thanks, ajdelange.

I thought that diacetyl was an issue in beers that were fermented too low and not allowed time to clean up in the fermenter, and that increasing the temps after primary fermentation was a way to get rid of that diacetyl. In my case, it seems like the yeast itself has a tendency to produce higher amounts of diacetyl even when fermented at higher temps. Does this layman have it right?

 

[ajdelange]

I thought that diacetyl was an issue in beers that were fermented too low and not allowed time to clean up in the fermenter,

It is.

and that increasing the temps after primary fermentation was a way to get rid of that diacetyl.

That is one way.

In my case, it seems like the yeast itself has a tendency to produce higher amounts of diacetyl even when fermented at higher temps.

As explained in #4 some yeast leak more precursor and some are better at cleaning up than others. In any case a valine poor wort leads to more precursor.

 

[kanzimonson]

I'm buying everything AJ is saying, but can you clarify one point: my understanding is that less diacetyl precursor is produced if you ferment low, and therefore it's easier for the yeast to cleanup.

 

[ajdelange]

I can't comment on that because I don't remember ever hearing that (doesn't mean it isn't true - just that I don't remember hearing it). It doesn't seem logical as if the yeast need valine they are going to synthesize it and at the same time diacetyl is often considered a problem in lager beers which are fermented cold.

 

[Brew_G]

ajdelange...thanks for the replies. Can you explain what you mean by "valine-poor wort" and how wort can be "valine sufficient" as compared to "valine-poor?"

All this scientific mumbo jumbo has me curious.