Acidulated Malt = Diacetyl?

[cdburg]

Well, given that you started at the right pH, and that every stage of beer making drops pH (including fermentation) I wouldn't think that's an issue either. What's the pH of your finished beer?

The pH meter is in the shop, but I'll take one when I get it back.

[spiderwrangler]

I can't see how acidulated malt can increase the amount of diacetyl. Diacetyl is made by yeast as follows-

Glucose is turned into pyruvate via glycolysis. Alpha acetolactate synthase then turns it into alpha acetolactate. In the presence of oxygen it turns into diacetyl. The presence of oxygen is important, which is why diacetyl is only produced during the initial stages of fermentation.

I don't think that oxygen is necessary for a-acetolactate to turn into diacetyl... a-acetolactate decarboxylates into diacetyl, no oxygen atoms are added...

[Afterlab]

2 -acetolactate undergoes Oxidative Decarboxylation to become diacetyl when diacetyl is reduced outside of the yeast cell walls and when it is reduced inside the cell wall it becomes acetoin. During oxygen uptake (when transferring from a fermentation vessel to a keg or bottles, diacetyl sees a temporary spike until it is once again reduced via extracellular and/or intracellular reduction. If you are, do not cold crash your beer at this state. If you keg it, add priming sugar to the keg and leave it at room temp.

I wouldn't waste time finding a strong and plausible connection with diacetyl and acid malt, you mentioned you don't a bacterial infection (Pediococcus) so this is a fermentation/packaging process issue. Diacetyl formation in beer has been studied and the metabolic process is generally agreed up. Either your beer isn't fully ready to be packaged when you package and consume it, your yeast isn't healthy enough to do its job properly or you're not doing a long enough diacetyl rest at the correct temp.

I have a hard time believing your post mash pH is so far out of the norm that it's having a large impact during fermentation. Yeast (brettanomyces especially) like a lower pH and attenuate to a higher degree with a lower pH. If you're using the a restrained amount of acid malt it shouldn't be dropping your pH that much. Even if your pH was too low, a low pH improves extracellular Oxidative Decarboxylation of 2-acetolactate to Diacetyl (This is good and should not be a problem), the problem is the yeast is not healthy enough reduce it, the pitching rate of healthy yeast isn't high enough, the temperature and timeframe isn't adequate for a diacetyl rest, there isn't a sufficient amount of amino acids or the head pressure in your vessel is too high and is causing the fermentation process to proceed slower than it should be.

Edit: Just for clarification, An Oxygen atom is not required for oxidation to occur. The term is misleading and in a simplified sense oxidation refers more to a loss of electrons during a reaction. The substance that losses an electron is said to be Oxidized and the substance that gains that electron is Reduced.

[cdburg]

While the diacetyl definitely could be due to yeast pitching amount, yeast health issues or insufficient time, it seems unlikely. That's why I'm asking about other possibilities.

All of these beers were fermented with new 001 vials grown into the appropriate Mr. Malty recommended starters. The most recent finished fermenting in about 5-6 days, and then sat on the yeast for another week before I crashed the temp to drop the yeast before dry hopping. It had plenty of time to cleanup. I'm also transferring from the conical to the keg in a closed transfer with the lines and keg all flushed with CO2. I don't think oxygen pickup there is an issue.

Though I think I've been vigilant, with my sanitation, unfortunately, an infection of some kind seems to be the most likely culprit. The transfer lines or kegerator draft lines seem to be the most likely places. I'm going to hook up the conical to a hot PBW loop and run it for a while. I'm cleaning the beer lines as well. If this batch is infected, it obviously won't help, but I hope to fix it for the next one.

Thank you everyone for your input!

[Afterlab]

While the diacetyl definitely could be due to yeast pitching amount, yeast health issues or insufficient time, it seems unlikely. That's why I'm asking about other possibilities.

All of these beers were fermented with new 001 vials grown into the appropriate Mr. Malty recommended starters. The most recent finished fermenting in about 5-6 days, and then sat on the yeast for another week before I crashed the temp to drop the yeast before dry hopping. It had plenty of time to cleanup.

Sometimes under ideal conditions it can take a full 20 days for diacetyl and it's precursors to be fully reduced.

Is it also possible that your palate has become better at detecting or has become more sensitive to diacetyl?

[cdburg]

Is it also possible that your palate has become better at detecting or has become more sensitive to diacetyl?

I've definitely become better at detecting diacetyl, which I suppose is the one benefit of this situation. The caramel/butter aroma and flavor is more faint in the last beer, but in the one before it, the diacetyl was terribly strong. It was an over-hopped IPA, and the butter totally overwhelmed the dry hop.

In each of the beers, I don't remember smelling or tasting the diacetyl in the conical samples. It's showing up in the keg. It seems like it's either an infection or something else that takes some time to build to levels I can detect.

I'm confident that the transfer process isn't exposing the beer to oxygen. Fermentation and transfer is all under CO2. It's either something picked up in the transfer or serving set up (infected lines) or another chemical process that takes longer to happen.

[Afterlab]

In each of the beers, I don't remember smelling or tasting the diacetyl in the conical samples. It's showing up in the keg. It seems like it's either an infection or something else that takes some time to build to levels I can detect.

Honestly sometimes the most logical reason is the answer and aside from letting the fermentation/maturation process go atleast 20 days before crashing, I would highly recommend priming in the keg, leaving it at room temp for 48 hours followed up by a very simple forced diacetyl test and then crashing in the fridge. Try it and if this doesn't work then I'm totally off base.

For shits and giggles, let's assume with all the alpha acids from this over-hopped IPA and the scarce amount of L.A.B. food remaining post fermentation. that this isn't a Pedio infection. Not to mention Pedio isn't going to make a strong and immediate foothold in a sanitized keg at refrigeration temps.

So fermentation is done, you've kegged under C02 pressure and thrown it in the fridge? So at this point it is safe to say that the remaining yeast enzymes are no longer creating new diacetyl or its precursors. So a highly probable scenario (excluding the presence of Pedio) of those diacetyl flavors appearing is that they're being synthesized later on in the keg. So this means there's a highly probable scenario that the precursor A-Acetolactate was still in solution when it was kegged. A-Acetolactate does not taste like diacetyl but it becomes diacetyl through Oxidative Decarboxylation when it loses electrons (CO2 off gasing). Normally this is not a problem during fermentation or bottled because you still have yeast working to reduce this at proper ale temps. This newly synthesized diacetyl does however become a big problem in a keg when it's created after you've crashed the yeast.

I'm confident that the transfer process isn't exposing the beer to oxygen.

Reminder - Oxygen is not required for oxidation reactions to occur.

[ScottyB-Brewing]

Wow that's a lot of chemistry right there.

My two cents is stop using the acidulated malt since you never had diacetyl before you started using it.