apalke

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I recently made an oatmeal stout and wanted to add a lot of chocolate and coffee flavors. To do this I added 8 oz baker's chocolate 5 minutes before flameout to melt the chocolate. We steeped 6 oz coffee a couple minutes after flameout.

I sampled the beer when I transferred to the secondary and when I bottled and both times it was spectacular... nice roasty toasty flavors as you would expect in a stout with a nice background chocolate flavor and slight aroma of coffee. A couple weeks after bottling the beer still tasted pretty good but not as great as I had remembered.

Now, maybe a month with the beers sitting in the bottles they've taken on a distinctly unpleasant sour flavor. I think I can rule out infection for three reasons:

-The beer tasted fine out of the bucket so at most only some of the bottles should have had some infection

-We've never had problems with sanitation and infections before or since

-After tasting the first batch from the bucket, I made a second batch and it also has the same unpleasant sour flavor. If some mysterious bug got into the first batch it's not extremely likely that it got my second batch too

My suspicion is that the oils from the cheap baker's chocolate I got from the grocery store went rancid with time sitting in the bottles. Maybe the slight exposure to air when bottling helped in this process? I've heard that chocolate oils can go rancid before, but I don't know exactly what to expect in this case. Anyone have any advice or suggestions?

Yooper

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"Sour" is almost always lactobacillus infection, or rarely aceterobacter infection.

Perhaps there was some headspace in the clearing vessel ("secondary") that allowed an infection to gain a foothold. The chocolate wouldn't go rancid.

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apalke

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But like I said, it happened in both of the beers which were in different secondary containers. And also like I said, I've never had any problems before with beers going sour. Except for the chocolate nothing much was different with these beers.

Maybe there were some bugs in the chocolate and I put it in too close to the end of the boil. If parts of the chocolate didn't melt until the temperature of the wort had dropped considerably there may have been some bugs in the middle of the chocolate that weren't wiped out by the heat? Does that sound more reasonable?

ReverseApacheMaster

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No not really. The chocolate would have still been pasteurized at 165F even if it hadn't completely melted.

It's more probable you have an infection somewhere along the way, whether it was in the bucket but slow to grow or in your bottling process.

FATC1TY

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Could be the fat in the chocolate... I'd suggest using a cocoa powder next go around, or nibs.

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seefish

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In the OP, you mentioned steeping the coffee a couple minutes after flameout. Could it have been below 165 by this point and some bugs hitched a ride on the coffee?

etrain666

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I have had a batch go bad after tasting great before bottling. After a bit of research I learned that you can pick up the infection at any point in the process. However, it may not have the time to really grow and compete with the alcohol until it has time to sit in the bottles for a while.

Do you get any gushing when opening the bottle?

apalke

Recipes 

The coffee was definitely not added below 165F. I just got the wort chiller going by the time I added the coffee. This also suggests that the chocolate would have been pasteurized as well.

apalke

Recipes 

The bottles didn't gush per se, but they were very carbonated with a thick head. If left in the bottle when opened they would bubble over a bit, but I had just chalked that up to using too much sugar in the priming solution.

I suppose it's not entirely impossible that both batches just happened to go bad one right after the other. It seems a bit unlikely, but not impossible.

I do think I'll use cocoa powder next time. From what I've read on the forums cocoa powder seems to be the preferred method anyhow.

Yooper

Recipes 

Definitely sounds like a lactobacillus infection.

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Giving beer a leg to stand on since 2006