Secondary ACTIVE fermentation in whiskey barrel?

So, I got a whiskey barrel from a boutique distillery here in Chicago. It had 22oz of whiskey still in it, which kept it wet (it was also kept sealed). I brewed up 30 gallons of Russian Imperial Stout, fermented it outside the barrel, and confirmed no more active fermentation (around 2 weeks)

FYI, 6 5 gallon batches were done

So, I drained the whiskey, transferred the beer, sealed it with a stopper and passed out from exhaustion! Woke up the next day with the stopper popped and fermentation started again! I was under the impression that since I fermented out I shouldn't have had any active fermentation in the barrel...

Was I wrong? Any idea if how much fermentation I should expect?

Are you sure it's actively fermenting, and not just released co2? I suppose the racking could have started up a stuck fermentation. Best way to tell is with hydrometer reading. Besides, there is no way of telling where it is at or when it will finish without this.

I've never used a whiskey barrel, but most barrels (this being an exception because it seems it recently had whiskey in it) have their fair share of interesting bacteria and wild yeast in them. Probably not the case.

I'm pretty sure...it has kreausen inside the bung hole (yes, that's what it's really called!) and I'm getting very consistent bubbling after putting on a blow-off tube...

2 of my batches were a bit high in their Final Gravity...I had already attempted to add yeast before transferring...as well as yeast energizer. Why would blending restart a stuck fermentation?

Not sure the blending would restart it, but the moving around of beer and yeast (racking), and the possible change in temperature (assuming a change from cooler to warmer) would.

Thanks for the info!

I rhink i knew racking can restart stuck fermentations, along with swirling the beer to disturb the cake (which I had done) so I just figured it was done

I guess I was mainly making sure that assuming the barrel was clean of yeast and bacteria, nothing in the barrel would be fermentable.

If it was still wet from a standard abv whiskey there were no contamination sources left alive in there.