Beer tasting good, then off/sour on second pour

[kmbell]

So I added coffee to my oatmeal stout and it's had this kind of sour off-flavor, I imagine from the acidity of the coffee. It's been like that since the week I kegged, which is when I first added the coffee.

Came back from vacation and pulled a beer, great flavor, could taste the melding of malts and coffee, no sourness. Same thing today, first beer was very good.

Only the *second* beer and every beer after has that sourness or weird flavor. Some flatness and lack of head, again from the second beer on. I would think that if it's in the lines the second beer would be better.

I had chalked it up to the coffee needing more aging, since the first one tasted good after not pulling a beer for a few weeks. But now I'm back to that sourness.

Might be some kind of separating between the cold brew and the beer that then gets mixed back together once it's poured a few times. Here are my thoughts:

1. Pour a beer from the tap
2. Pour a second beer
3. Taste directly from the keg (open it up and take some beer)

Solutions:

4. Replace tubes and disassemble faucet to clean
5. Clean and disassemble keg for sanitizing (ideally I'll find the problem and not have to dump anything)

Anyone ever have a similar issue?

 

[schematix]

Oxidation perhaps? Did you open the keg lid to add the coffee?

 

[kmbell]

I only had the keg open to add beer and coffee initially and I purged the headspace

 

[schematix]

Someone will probably chime in and call me a proselyte (apparently oxidation a touchy subject around here), but purging is not sufficient to stop oxidation. Air is about 21% oxygen, and it only takes amounts measured in the parts per billion to cause oxidation. When you purge all you're really doing is diluting whats in there.

That may not definitively be your problem, but it is suspect. I used to get a sour-ish flavor in my beers when i would ferment in buckets then rack through the keg lid. The more i reduced exposure, the better it got, but never eliminated until i went to closed pressurized fermentation and racking.

If you do this again, add the hot coffee at the tailing end of fermentation, then rack to the keg with a few gravity points left, seal it up, and let it finish fermentation for a week or two to get the natural carbonation. Not only will the carbonation be better, but you'll have a keg nearly devoid of oxygen.

 

[kmbell]

Any idea why this would be more noticeable on this beer, a dark oatmeal stout, that wasn't present during my previous ones?

I'll also try tightening my fittings, I had a similar weird carb issue that had to do with incomplete seals from not tightening the fittings enough

 

[Hoppy2bmerry]

I'm following... What kind of coffee did you add? Pasteurized cold brew, or strong hot brewed? Any time I have tasted oxidation in my own brews (I think I have my bottling procedure improved to avoid those couple off bottles) I would not describe is as sour old funky coffee can have a weird taste. I have also just bottled a coffee Porter using a cold brew concentrate from Trader Joe's, so eager to hear more opinions and info from OP.

 

[kmbell]

What I did was a strong cold brew from home roasted beans.

It could still be the old coffee flavor, but I'm still at a loss to explain why it went from funky coffee then three weeks later to pouring one perfectly topped great-tasting beer and then back to more funky coffee flavor with no foam.

 

[kmbell]

It was 16 oz of cold brew in 3 gal or roughly 5%

 

[Hoppy2bmerry]

I decided to use the coffee as my priming addition and maple syrup warmed in microwave so I wouldn't have to heat the coffee. But you are right, unless it's getting funky in the lines? I know I'm just grabbing at straws, but is at least gives the thread a bump