Interesting off flavor...anyone have ideas why?

So this is a weird one. I have an off flavor that is actually GOOD, but I am not sure how this happened. Trying to sleuth this one out; anyone have a similar issue or know what's going on?

I brewed an old ale. It tasted fine when sampling throughout the process. I follow strict clean/sanitary procedures and am on point.

I aged it on some cognac soaked virgin white oak for about 9 months. I soaked the oak in cheap cognac and discarded the tannin rich liquid and then re-soaked in very good cognac to condition prior to adding it to the beer for aging.


The beer tasted as it should in every step of the process; even during aging of the oak until the last week when it was getting very close to the flavor profile I wanted from the oak aging; it was right where I wanted it and I decided to bottle. The sample I took just before bottling- took on a subtle sour flavor.

The thing is; it tastes wonderful; and as the bottles have aged it is getting more complex; not "Stronger" per say, but the sour flavor is changing a bit At first it was very subtle and oaky sourness; then the sour was very forward with less oak; now the sourness is soft and balancing well with malt/hops/oak (In bottles for about 4 months now). It tastes like a barrel aged sour old ale; that was deliberately soured very slightly.

I didn't use any bugs (on purpose).

The only thing I can think would have done this would be bugs in the oak, but I would think the cognac soak would kill those bugs- no?

Of course it could be infection not from the oak itself, but something that snuck in when adding the oak. Not at bottling though, as it had already taken on this flavor prior to bottling.

Usually when I have an off flavor I am able to pinpoint it by going over notes, tasting and detecting the culprit. This one kinda has me baffled as my practices were sound. Only thing I can think of is a random infection, or the wood had bugs and the cognac didn't kill them.

Anyone had this happen before? Any thoughts?

No rings around bottle necks, no gushers, nothing that jumps out and says "infected" beer. Has wonderful head retention, great velvety mouth-feel, full body and balance.

I'm happy the beer isn't ruined as I put a lot of money and time into this one, but I would like to figure what is going on.


Thoughts?

-Edited to add:
There was no pellicle or any visual indication of a bug/infection in the beer.

 

I used virgin oak; non toasted/charred.I looked at the recipe and I did use 1/2 lb of roasted barley; which was steeped and then added to the wort just before boil.

Here's the recipe and process I used if it gives anyone a better idea of what may have happened.

5 gallon batch size
Target OG: 1.085
Target FG: 1.009
Single Infusion Mash 154 F
Batch sparge

12 lbs. British 2-Row
3/4 lbs. Crystal 60L
1/4 lbs. Chocolate (1/8 lb dark & 1/8 lb light)
1/4 lbs. Flaked Barley
1/2 lbs Roasted Barley (Steeped and added prior to Boil)
3 lbs. Light DME

1.5 Oz. Fuggles (5.0%) @ 60 Min
1 Oz. Fuggles (5.0%) @ 20 Min
.5 Oz. Willamette (5.5%) @ 15 Min
(1) Whirfloc Tablet @ 15 Minutes
.5 Oz Willamette (5.5%) @ Flameout

2 L Starter of WLP-013 London Ale Yeast. 1 Minute oxygenation with pure oxy/diffusion stone

Actual OG: 1.088
FG: 1.004

Aged on 2 Oz. Cognac soaked American White Virgin Oak for 9 months after primary ferm ceased.

 

Never implied it was a "problem". Trying to reverse engineer what happened, as it might be something I'd like to reproduce if possible. If it was a combo of ingredients and process making the flavor I could definitely reproduce that; if it is wild yeast then it would be very hard to reproduce.

The FG is low for the grain bill, so leaning towards wild yeast makes sense and that was my first thought also. Ijust can't figure out how wild yeast could have gotten in.

Are there strains of wild yeast that can survive being soaked in high proof liquor for weeks? Because the oak is the only thing I can pin point as a possible supplier of the wild yeast.

I know there are other ways for wild yeast to get in, but I take crazy precautions to keep things like this from happening.

Thanks for all the replies.

Take care gents.

 

I keep my bottles in a room that sits at about 66 F to condition.

 

That's a good idea, thanks. I'm going to do this and see...