Diacetcyl

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Homercidal

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So Brewed an Amber the other day and it turned out very buttery. At first I thought it was just the excess caramel malt, maybe the copper malt I got from NHC.

I needed a beer to submit to a club competition as an "Autumnal Seasonal Beer" so when I got home last night I hot steeped some spices in a small pan and added a bit of sugar (The beer was not sweet enough without), strained the liquid through a coffee filter and added 9 ML to each bottle as I filled from the keg.

Although the beer was buttery/butterscotchy I submitted to see what the club members would think. They pretty much all said they tasted butter. And slickness. Just as I did.

So now I want to understand better how it happened. I am pretty sure I know, but I thought it might be helpful to describe what happened so others can understand and prevent it.

First, my recipe called for a good amount of caramel malt. I think I ended up using 1.5-2 lbs caramel malt. 1 lb of Briess Copper and like 1/2 lb of crystal 40 IIRC. Unless I'm mistaken, this helps provide the Diacetyl precursors.

Secondly, I fermented S-04 at about 62. Now normally I don't really have a problem fermenting S-04 that low. I believe it's not out of the recommended range for that yeast, but there's more:

I let it ferment out, and then while the beer was still young I racked into a keg and placed in my kegerator. This is what I believe was the real trouble. I likely racked and chilled at just the wrong time for Diacetyl. I'm betting it was at the maxmium level.

What I should have done is to rack to the keg and let it warm up for a couple of days, or simply raised the temp in the fermentor for a few days before racking. The yeast had no opportunity to clean up after themselves as the immediately got sent to hibernation.

There may be other causes I am not aware of, but if anyone can think of anything I missed, please reply. I am guilty in this case of being too hurried. I really had nothing to lose by letting the beer warm up to room temp for a couple of days before kegging.
 
I'm not sure about the caramel malt having more SMMs than other specialty malts, but you could be right about that.

I do tend to get more diacetyl with English yeast strains (and English beers often have a tad of diacetyl as part of the character), but S04 even at 62 degrees has never given me diacetyl. And generally, S04 is a fast fermentor and flocculates and drops clear within a day of reaching FG, so I'm not sure that not kegging it when you did was an issue either.

Ha- I just reread what I wrote and all I basically said was "I don't know"................ Sorry about that. But I really don't.
 
I'm not sure about the caramel malt having more SMMs than other specialty malts, but you could be right about that.

I do tend to get more diacetyl with English yeast strains (and English beers often have a tad of diacetyl as part of the character), but S04 even at 62 degrees has never given me diacetyl. And generally, S04 is a fast fermentor and flocculates and drops clear within a day of reaching FG, so I'm not sure that not kegging it when you did was an issue either.

Ha- I just reread what I wrote and all I basically said was "I don't know"................ Sorry about that. But I really don't.

No problem. I'm not sure it's SMM that causes Diacetyl. SMM is a precursor for DMS, which is vegetable-like flavors. Hold on, let me look it up...


The information I have is that the yeast generate Valine, and in doing so generates Acetolactates, some of which leak out during the process. Some of this Acetolactate is a Diacetyl precursor.

I think the important point is that it's possible to limit some of the leaking through yeast nutrients, but that the amount of Acetolactate that is generated is often dependent on the yeast strain. So maybe it's not as much the caramel malt that adds to it? I do know that some caramel malts mimic the flavor of butterscotch to a certain degree, but in this case it's obviously in excess of what would be considered normal in this kind of beer, hence my looking elsewhere for causes.

One other thing to mention is that some bacteria can cause Diacetyl as well, including Pediococcus and Lactobacillus. Now I doubt this is the cause in this case since it happened so quickly and under my usual cleanliness while brewing. Also, the flavor doesn't have a nasty edge to it, or sourness. It's just a malty amber ale with pronounced butterscotch flavor.

One thing I've been doing lately, to my admitted detriment, is to keg too quickly after fermentation, directly from the fermentation chamber. I have to believe this is the main culprit. Sometimes I do this due to a rapidly approaching deadline, like for a beer festival or competition. Planning farther out would help this. Sometimes I'm just in a hurry for no good reason, as in this case. I've never had such a pronounced buttery flavor as this, though. I've done plenty of IPAs and other pale ales without really noticing it. I believe I'm not that sensitive to the flavor, TBH. So this must be really noticeable to others.

I am now rethinking my process of moving beers from fermentor to keg. Having kegs makes things so much easier, and I admit I like being able to take an empty keg, clean it, and refill it all at the same time. However, I might hold off on putting it in the kegerator for a few days to help with this.

I'm kind of anxious to rebrew this batch and see what happens. I think I have all of the same ingredients, except I am out of Pale Malt and instead have Marris Otter on hand. I could very easily salvage this beer into a storage container to re-process later into something else...
 
Also, I don't always aerate my wort. For beers at less than 1.050 gravity (ish) I might just pitch a whole packet of yeast onto the wort. I don't recall if I did that this time or not. Besides, I think it was Chris White who claims that aerating wort is unnecessary for dry yeast, as they have supposedly already created the sterols they need during the dehydration process.

Aeration, or lack thereof, is listed as one possible contributor. When filling my fermentor, I usually have my pump splash the wort into the fermentor while I hold the filling tube up in the air above. This causes a pretty significant agitation, but of course it's nowhere near as effective as using an O2 stone, which I have and will use for bigger beers or Lagers.
 
Hmm.. Is there nothing else to consider?

I'm seriously thinking about rebrewing this to see what happens with the same yeast, temps, etc., but add a diacetyl rest. I had some again last night right from the tap and it was plainly buttery. Instead of throwing it away or re-purposing, I might bring it out of the kegerator, stir it up, and let the yeast do their thing, if they are going to.
 
Hmm.. Is there nothing else to consider?

I'm seriously thinking about rebrewing this to see what happens with the same yeast, temps, etc., but add a diacetyl rest. I had some again last night right from the tap and it was plainly buttery. Instead of throwing it away or re-purposing, I might bring it out of the kegerator, stir it up, and let the yeast do their thing, if they are going to.

The only other thing to consider (in my opinion) is one you already mentioned- a low level pediococcus contamination. Or something else that stressed the yeast (low zinc?).

Since that yeast may produce diacetyl in abundance like other English strains, that could be a part of it as well although I've never had that happened. I rarely use that yeast strain, though, since I think it tastes sort of weird and used all the packages I have in cider since it's great in cider.
 

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