Another Q about diacetyl

[brad451]

I just bottled a Belgian style Ale that was made from 85% pilsner, 10% wheat, 5% invert sugar; Wyeast 1388. OG was 1.08; after 4 weeks in the primary it came down to 1.01. So attenuation was in the upper 80's. I took a sample from the primary (@ 70F) and it seemed fine. That is to say, there were no off flavors and definitely no detectable diacetyl. So, certain that fermentation was done and that the beer had already gone through a sufficient diacetyl rest I decided to bottle. But I gave it another 48 hours to be 100% certain. While I was racking into a bottling bucket I pulled a quart off to taste it one last time. This time it was slick as hell, greasy like a fat pork shoulder. Where did the diacetyl suddenly come from? Is it possible that the diacetyl was stratified in the primary fermenter? My original sample on Sunday came from the top of the fermenter; the sample I took yesterday came from the bottom near the trub. In fact, the trub was disturbed a bit by my racking cane. Is that a possible source? And will bottle conditioning clean it up?

 

[brad451]

Ok. Since no one has responded to this thread yet I am going to add a few more thoughts. I was thinking that *possibly* there was an abundance of alpha-acetolactate in my beer that hadn't yet undergone decarboxylation and that opening the fermenter top introduced the oxygen that a-acetolactate needed to fully decarboxylate. Does that sound reasonable? I always understood that decarboxylation was spontaneous, but that oxygen was necessary for the process to happen. Or maybe oxygen is not a necessary catalyst for decarboxylation. So does anybody know if higher gravity beers can slow down or even halt decarboxylation?

 

[notwoohoo]

I'd consider contamination as a possible source, even in this high gravity beer. Both pediococcus and lactobacillus will throw diacetyl, which can come on quickly. How was your sanitation regime when pulling your taste sample? If it turns out to be contamination, it is probably a loss (you could always pasteurize and bottle, but I wouldn't have high hopes).

 

[brad451]

I boiled my instruments for about 15 minutes before I took a sample. Other than having the fermenter open for the 60 seconds it took to get the beer out to test I don't know how it would have become contaminated. It's in bottles now, so I'll just wait and see. I did consider contamination; I just thought there might be a chemist lurking around here that could shed some light on things.

By the way: Can you direct me to some material explaining how the two bacteria you mentioned affect diacetyl?

 

[Lil' Sparky]

I can't give you a difinitive answer, but I doubt it's contaminated. All I know is beer goes through all kinds of weird changes as it ferments, clears, and bottle carbs/conditions. I bet it has something to do with the stratification issue, or something in the trub you stirred up. I wouldn't sweat it.

 

[brad451]

Does diacetyl production ever really come to an end? I know that some breweries use an alpha-acetolactate decarboxalase enzyme for that reason. Anyway, I'm with you Sparky. I don't think it is diacetyl (especially after talking with a chemist friend about it.)
I'm also thinking less about contamination today and more about proteins. Actually, I am starting to think about the presence of lipids (triglycerides and fatty acids) derived from the wheat gluten. I've seen a few studies that have discussed the presence of lipids affecting head retention and late off-flavor development. One study found that the presence of triolein and palmitic acids decreased head retention. [link below] Pretty sure that lipids can rot like corn oil too(can they be carcinogenic?) causing the off flavors. But I haven't read anything directly saying that lipids can cause slickness, although it seems logical that in high concentrations they would.


Food Proteins and Their Applications - Google Book Search

 

[Cpt_Kirks]

I'd consider contamination as a possible source, even in this high gravity beer. Both pediococcus and lactobacillus will throw diacetyl, which can come on quickly. How was your sanitation regime when pulling your taste sample? If it turns out to be contamination, it is probably a loss (you could always pasteurize and bottle, but I wouldn't have high hopes).

I had that happen. An amber lager that had no noticeable diacetyl at kegging was buttery as microwave popcorn a few days later. I have become pretty fanatical about sanitation since.

Since that was a kegged batch, I was able to clean most of it up with a US-05 starter dumped into the keg. It wound up being a fairly nice, drinkable brew.

 

[brad451]

I have to say (with my meager knowledge of biochemistry) that both pediococcus and lactobacillus should, in addition to producing diacetyl also produce a lot of lactic acid. I didn't detect any of that in this beer. But I am still very much interested in a description of the metabolic pathways of both of those bacteria if anybody has some info on that.