Eagle-eyed imbibers enjoying a fresh bottle of Deschutes’ superb Hop Henge Experimental IPA this past weekend might have noticed a little note on the side saying “Batch 3.”

That’s because — not surprisingly — the current bottling run is the third and final version of the sublimely delicious Hop Henge to be brewed this spring.

Each run has been slightly different as the good folks at Deschutes have tried to achieve a goal of 95 IBUs per bottle. That, of course, is the acronym for International Bittering Units. Each batch of the Hop Henge has featured more and more IBUS, with Batch 3 topping out at 91.

Deschutes Brewmaster Larry Sidor had been experimenting with different hop and malt combinations to make this year’s Hop Henge “A teeth-staining, mouth-numbing, tongue-scraping IPA that would impress the most iron-lipped hop head,” according to the Deschutes blog.

Check out the blog to get the whole story of this year’s Hop Henge experiments, which include a literal hop explosion during the brewing of Batch 1 — check out the photo.

Long story short — the first batch of Hop Henge was about 80 IBUs. Batch 2 got up to 87 IBUs. Batch 3 is 91 IBUs. All are “wild with hops,” Sidor told me Monday.

I’ve had all three versions, and they are all fantastic — good enough for me to smugly tell my brothers in Ohio, who can’t get Deschutes, how good they were. The citrusy hop aroma leaps out the glass and the smooth and complex bitter finish of the Hop Henge is extraordinary. It’s my favorite beer of 2009 so far.

Sidor said Monday there was a detectable difference with the bitterness between Batch 1 and 2 but not much between Batch 2 and 3. He moved the beer out of the fermentation tank a little earlier but the recipe is essentially the same.

I’d love to hear from any of you guys if you drank them and noticed a difference, or have a favorite.