Help! Diacetyl!

[soggycd]

My brews have been tainted with diacetyl recently, ales and lagers, and I cannot fathom why.

I control my fermentation temps religiously, I am confident in my sanitation routines, I ferment and store in glass and kegs, and I always pitch plenty of yeast.

Does anybody have any ideas where the diacetyl could be coming from? This is a recent problem, but I have not been doing anything different fermentation wise, as far as I know, for a while now. I am at a loss of ideas.

 

[ajdelange]

Yes, I have a pretty good idea where diacetyl comes from - leakage of alpha-aceto lactate from the valine synthesis pathway which survives into the package where it is oxidized (non enzymatically) into diacetyl. At least that's where we hope it is coming from because you can get rid of it if it is. If it is 'sarcina sickness' from pediococcus or some other spoilage organism then you are pretty much SOL (to use the technical term). But as you are confident in your sanitation practices we assume that is not the case. There are hundreds of posts here on how to deal with normal diacetyl prodution. I'll only sumarize them breiefly:
1. Conduct fermentation and lagering according to the traditional German methods.
2. Employ diacetyl rests (elevated temperature at the end of fermentation)
3. Krausen.

 

[WayFrae]

I know you said you always pitch plenty of yeast but maybe you aren't. I believe under-pitching yeast is the most common cause of excessive diacetyl.

 

[soggycd]

To AJ: I ferment and lager according to traditional german methods as far as I know (german beers are my favorite so that's what I try to emulate) and I do diacetyl rests. I have never tried krausening, but my understanding is that this is a problem fix, which is a good tool to have I am sure, but that it should not be required if the beer is brewed properly.

To wayfrae: I use temp controlled fermentation chests, and I almost always have signs of fermentation within 6 hours. Other than warm temps, which I do not have, I do not know what would cause fast fermentation other than plentiful yeast counts.

 

[ajdelange]

Infection aside the most common source of a diacetyl problem is no yeast to take it up after a-acetolactate converts to it in the package.

 

[ajdelange]

To AJ: I ferment and lager according to traditional german methods as far as I know (german beers are my favorite so that's what I try to emulate) and I do diacetyl rests.

Then you shouldn't have a problem (nor should you need a diacetyl rest) so we begin to suspect infections.

I have never tried krausening, but my understanding is that this is a problem fix,

You shouldn't need it but it is a common practice. One way or another one needs to have active yeast available after the diacetyl is formed. If lagered with plenty of yeast in the lagering vessel, if krausened or if the yeast are kicked into high gear by a temperature increase that active yeast is available.

 

[soggycd]

Infection aside the most common source of a diacetyl problem is no yeast to take it up after a-acetolactate converts to it in the package.

This is the most convincing idea I have come across. I do a pretty good job dropping bright my beers, maybe too good? Perhaps I am removing the yeast too soon. Seems like two weeks in the primary would be enough, but perhaps that is something to experiment with.

You shouldn't need it but it is a common practice. One way or another one needs to have active yeast available after the diacetyl is formed. If lagered with plenty of yeast in the lagering vessel, if krausened or if the yeast are kicked into high gear by a temperature increase that active yeast is available.

Does lagering remove diacetyl? I thought yeast had to be active/warm to metabolize diacetyl.

 

[soggycd]

Do water conditions affect diacetyl production? I know my water profile more or less, never measured my wort ph tho.

 

[ajdelange]

This is the most convincing idea I have come across. I do a pretty good job dropping bright my beers, maybe too good? Perhaps I am removing the yeast too soon.

Light comes on. Yes, I'm guessing you are. It is imperative that the beer enter the lagering vessel with lots of yeast. Definitely transfer before the beer has dropped clear. This is for the traditional method. If you do a diacetyl rest then you are not relying on yeast action in the lagering phase. In this case make sure there is plenty of extract (a couple of degrees) for the yeast to consume during the diacetly rest. If the diacetyl rest has been successful then you can crash cool and package.

Does lagering remove diacetyl?

Yes, definitely. If yeast are present. That's why you need to make sure there are. And some say that you have to augment the surface area over which the yeast have access to the beer. That's what 'beechwood aging' is all about. Home brewers often lay Cornies on their side to give the yeast access to a larger area of the keg.

I thought yeast had to be active/warm to metabolize diacetyl.

No, not at all but, of course, they'll do their work faster at higher temp. That's why a diactyl rest is a day or two but lagering takes months.

Water would have no effect (that I can think of).

 

[soggycd]

Thanks aj. I think we have a good working hypothesis.