Due to the inherent variability in aging beer, most barrel aged liquids are actually blended together before bottling time. Those angels are thirsty, but they don't drink equally from each barrel, not to mention that moron Randy from Accounting1 who is constantly trying to sneak a sample of your latest barrel aged brew.
This is generally the case with anything aged in barrels. Some of the complexity in Scotch comes from the fact that different barrel types and ages are blended together into the final product. Of course, there are beers that are all about the blend too, like Gueuzes, and there are others that are blends of completely different beers (a la Firestone Anniversary beers). But even your lowly, garden-variety bourbon barrel aged stout gets some blending love (i.e. the contents of each barrel are combined into one mass) before bottling, thus evening out the batch and ensuring some form of consistency.
Naturally, there are exceptions. I have a bottle of Balvenie 15 that is utterly superb, but that's a Scotch bottled from single barrels. No blending. They don't even claim consistency and actually use the variability as a selling point: "Each bottle is unique and unrepeatable." This appears to be DuClaw's strategy for Retribution, a single barrel bourbon aged imperial stout. Let's see how that turned out for them.
DuClaw Retribution - Pours a very dark amber brown that pretty much looks black once poured out, with half a finger of light brown head. Smells strongly of bourbon, with some vanilla, caramel, and oak asserting themselves. The taste is extremely sweet, with plenty of that bourbon and vanilla character, some caramel, a little chocolate, and plenty of sticky booze in the finish. Mouthfeel is sticky, medium bodied, boozy, a little light on carbonation (but just barely enough to make this palatable). Maybe a bit on the cloying side as I near the end of the bottle. Overall, it's a fine barrel aged beer, but not among the top tier. I wonder if it would have been better fresh (or if barrel 8 was a dud). B
Beer Nerd Details: 9% ABV?2 bottled (22 oz. bomber). Drank out of a snifter on 11/4/12. Label sez: Date in Barrel: 03/11/2011. Date Out of Barrel: 09/19/2011. Barrel No. 08 of 20.
So I like DuClaw and ultimately enjoyed this, but they're no Balvenie. Despite the assumed variability, I'm not sure I want to pick up other bottles of this, though I wouldn't mind sampling it if I ever end up in one of their brewpubs or something. Also, they apparently make something called Divine Retribution which is a blend of Retribution and their massive 21% ABV Colossus. Yikes.
2 - The bottle I have in front of me right now sez 9% ABV, Beer Advocate and Ratebeer say 10.5%, and DuClaw's website clocks it at 11.5%. Perhaps barrel 8 really did suck and only came in at 9%, or this 2011 batch came in lower than expected or something.