Acidulated Malt = Diacetyl?

[cdburg]

Over my last few batches, I've had problems with diacetyl in the finished beer. I've been all grain brewing for about 6 years, and diacetyl hasn't ever been a problem until recently. I'm trying to figure out what may have changed in my recent beers, and I've narrowed it down to two options: 1) The use of acidulated malt 2) Use of a stainless conical

I recently purchased a pH meter, and, as a result, have been paying more attention to the mash pH. I've been adding acidulated malt to get the mash pH to the 5.3 - 5.4 pH range. This has required the use of 2-4% acidulated malt in the mash, which I think may be the problem. The final beers, once the hops begin to fade, have had either a strong buttered popcorn aroma and flavor (in the earlier bad batches) or a stronger than expected caramel/toffee flavor (the most recent batch). The most recent batch had no "traditional" crystal malt in it - only two row, white wheat, and carafoam.

I've also recently started fermenting in a conical. I really don't believe this is the cause, since I've fermented the beers, all using Cal Ale 001, at 65F to 68F with a raise to about 71F at the end to push the yeast to finish their work.

I've bought new tubing for transfers and I have no reason to believe my sanitation is the cause. I keep coming back to the acid malt, and am planning to drop it from my new batch. I'm thinking of either letting the pH go or using phosphoric acid instead.

Has anyone else has diacetyl issues that might have resulted from acidulated malt? Any other thoughts?

[mabrungard]

I recall reports that fermenter shape and depth having an effect on beer quality, but I don't recall it having anything to do with diacetyl. It was more like esters that are affected if I remember correctly.

I can't imagine that the acid malt had anything to do with it either since it is just pale malt with lactic acid infused. Sorry I can't help out with your issue. One other thing to consider is an infection with a diacetyl producing organism.

Certainly do test your variables to see if you can isolate the cause. I do recommend that you continue to acidify as necessary to bring your mash and sparging water pH's down to proper levels since they affect several beer quality parameters.

[cdburg]

I can't imagine that the acid malt had anything to do with it either since it is just pale malt with lactic acid infused. Sorry I can't help out with your issue. One other thing to consider is an infection with a diacetyl producing organism.

I'm not finding much in my own research, but I have found a few references in BJCP study material to extended acid rests leading to diacetyl. Since an acid rest is just creating lactic acid, from what I understand anyway, one of my guesses was that too much acid malt was contributing too much lactic acid to the wort, and either the yeast can't deal with it properly, or something else happens that ends up with it becoming diacetyl.

I'm definitely going to give the conical another thorough cleaning and sanitizing. I'll do the same with the transfer lines and serving lines. I'm leaning toward using just phosphoric acid in the next batch for the pH adjustments to see if that makes a difference. I'd rather not just let the pH be an uncontrolled variable.

[peas_and_corn]

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.

[cdburg]

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'm guessing that it might be more of a situation where a low pH may have stressed the yeast and caused it to not reabsorb the diacetyl produced during fermentation. It wouldn't be that the acidulated malt directly caused the diacetyl, but that it contributed to a pH that made the yeast less effective in cleaning up after itself. It's definitely a pretty blind guess, but I'm really unsure as to why this is suddenly a problem for me.

I'm definitely going to clean the kegerator lines tomorrow as well, to make sure it's nothing with an infection causing it.

[peas_and_corn]

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?

[mabrungard]

I didn't see a smoking gun, but I do see some linkage when I search for lactate and diacetyl. There may be some sort of metabolic pathway to diacetyl from lactate. Of course, lactic acid leaves the lactate ion in solution and it could be subsequently metabolized. I didn't see a specific description on the process, but it looks possible from all the discussion on that subject.

So, maybe the acid malt (lactic acid) is fueling the diacetyl production. Do explore using phosphoric acid since that will reduce the overall lactate ion content in the wort and beer.

[cdburg]

I didn't see a smoking gun, but I do see some linkage when I search for lactate and diacetyl. There may be some sort of metabolic pathway to diacetyl from lactate. Of course, lactic acid leaves the lactate ion in solution and it could be subsequently metabolized. I didn't see a specific description on the process, but it looks possible from all the discussion on that subject.

So, maybe the acid malt (lactic acid) is fueling the diacetyl production. Do explore using phosphoric acid since that will reduce the overall lactate ion content in the wort and beer.

I had the same thought when I listened to one of the Brew Strong water shows you did with Jamil and John, maybe the one where you talked about water for Hefeweizens. I have soft water, so I'm guessing (key word) too much acid malt leads to excess lactate in the water, and as you said, it may somehow be converted to diacetyl. It's all just a guess at this point. I'm definitely going to go with phosphoric in the next batch to try to remove that variable. I'll post back with the results. I'm also going to double down on sanitation to make sure it's not an issue with an infection.