Acidulated Malt = Diacetyl?

[cdburg]

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.

It sounds like a split batch with half getting primed in the keg and the other half being force carbonated normally could be in order. If the primed half is ok, and the force carbonated version is not, we have the answer, seemingly. If both are ok, the tweak I will make to the recipe to remove the acidulated malt would seem to have been the fix. If neither are ok, sanitization or a poor initial ferment would seem to be the cause, still.

Thank you for the suggestion!

[cdburg]

Wow that's a lot of chemistry right there.

I agree. This thread has been very helpful. I've had to do some research to understand, somewhat anyway, but the discussion has helped with some ideas.

[spiderwrangler]

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

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

Yeah, what Spider said.

[EagleDude]

Great Discussion! After reading through it all ... I almost lean toward the issues with pedio in your tap lines. To rule out diacetyl coming from the fermentation side of things or left over alpha-acetolactate that later turns into diacetyl through oxidation, I would suggest the following:
1. taking a 2 samples from the fermenter and set 1 aside.
2. Place the 1 sample in a hot water bath of about 150 degree water.
3. Drink a beer or two (~20 minutes).
4. Place the heated sample into an ice bath to cool back to the temp of the original sample.

Result options:
1. both samples show no signs if diacetyl, you are good to go.
2. The heated sample has diacetyl but not the control, then you still have excess acetolactate and need to continue with a diacetyl rest (ramp temps up and give it a few days).
3. If both samples have diacetyl, pedio in the fermenter may be the problem (I would still try a diacetyl rest to see if thing cleared up).


Finally, the above test turns out great with no diacetyl but you end up with it after transfer to kegs and dispensing, then the pedio infection is in the dispensing side of things --> clean lines, replace plastic/rubber hosing and o-rings, sanitize everything metal, etc.

Hope this helps a bit and please keep us posted on what you figure out. I have been using a conical for the last 6 years, am super sensitive to diacetyl, and never had a problem with it, so the fermentor shouldn't be the cause.

[cdburg]

Great Discussion! After reading through it all ... I almost lean toward the issues with pedio in your tap lines. To rule out diacetyl coming from the fermentation side of things or left over alpha-acetolactate that later turns into diacetyl through oxidation, I would suggest the following:
1. taking a 2 samples from the fermenter and set 1 aside.
2. Place the 1 sample in a hot water bath of about 150 degree water.
3. Drink a beer or two (~20 minutes).
4. Place the heated sample into an ice bath to cool back to the temp of the original sample.

Result options:
1. both samples show no signs if diacetyl, you are good to go.
2. The heated sample has diacetyl but not the control, then you still have excess acetolactate and need to continue with a diacetyl rest (ramp temps up and give it a few days).
3. If both samples have diacetyl, pedio in the fermenter may be the problem (I would still try a diacetyl rest to see if thing cleared up).

I'll definitely go with a diacetyl test before I keg. A thorough cleaning and/or replacement of parts is also underway. I'm not able to brew as often as I'd like lately, so the next batch may be a few weeks away. I'll post back with updates when I am able though.

[cdburg]

Quick update on this... I brewed another IPA last Friday. Fermentation started at 66F, and I let it rise to 71F gradually. Active fermentation was done after 6 days. I've given the batch another few days on the yeast to make sure everything is cleaned up.

I ran a forced diacetyl test this morning. I left a covered sample in hot water for about 30 minutes and then smelled/tasted for diacetyl. I couldn't smell or taste any diacetyl, so I'm hoping I'm good to go. I'm going to crash cool the batch at 55F to drop the Cal Ale yeast and then start the dry hop.

[cdburg]

I've had my most recent IPA on tap for about a month, so I'm pretty confident in saying that it doesn't have the same diacetyl issues the previous batches did. The only recipe change I made was to remove the acidulated malt. I used Rahr 2 row instead of Great Western, which I've ready produces a slightly lower pH. The mash pH was 5.45, which was exactly what I was aiming for using Bru'n Water. I also got a replacement pH meter for this batch, since the previous one stopped working. I'm wondering if that played a role in the diacetyl problem too.

In terms of process, I ran the forced diacetyl test, as I mentioned earlier. It came back clean. The timing of the fermentation, cold crash, and dry hop were about the same.

It's obviously impossible to know, definitively, but I do think the acidulated malt and/or pH issues in the mash somehow played a part in the diacetyl. I'm not entirely sure how, but it seems to be the variable that carried through the bad batches and was resolved with this one. I guess I'll see if it continues to resolve the issue going forward.