I haven't seen any and would love to try one, but more importantly has anyone made one already? Is there something about grapefruit that would not do well aging in a sour barrel?
Hmm.. you mean age a beer with actaul grapefruit juice added? I think the acidity of grapefuit may be too high for that to work.
The first one that comes to mind is Stiegl Grapefruit Radler which is basically a mix of Goldbrau and grapefruit soda. It's tart, with low abv (I think under 3%) and drinks like a fizzy Berliner. Not bad on a hot summer day, but I'm guessing you were thinking of more like a Cascade-type sour, and I've yet to find one like that. http://www.beeradvocate.com/beer/profile/817/68049/
I was just at Arizona Wilderness Brewing Co. last week and they had a Grapefruit Berliner. Available for growler fills as well. It was pretty good. http://www.beeradvocate.com/beer/profile/32656/113517/
Not quite what you're asking, but New Belgium Le Terroir does taste like freshly squeezed sour grapefruit and oranges (from the dry hopping).
There is this one from 10 Barrel which I really enjoyed: http://www.beeradvocate.com/beer/profile/16873/93805/?show_ratings=N
4 Hands Ruby Red Prussia, its a Berliner and pretty good, well at least better than some of the reviews would have you believe http://www.beeradvocate.com/beer/profile/27870/98376/
Just saw Abita Grapefruit IPA on a shelf. That is almost surely just an IPA with grapefruit added to it. It might be good, who knows?...but I didn't give it a go.. EDIT: Just saw the "Sours" in the title. Was reading through quickly, sorry...I'm stupid
Always wanted to try a nice grapefruit sour. Mentioned it to the guys at the Rare Barrel recently so maybe they'll experiment? They've been using a fair amount of different fruit for a brewery that's only been open a few months (though I know they have been aging beer for a while before they opened).
Check out WWB Batch 60 from Crooked Stave. Most grapefruity sour I've ever had. Kept expecting to feel grapefruit pulp stuck between my teeth after each drink.
you could always find the cheapest Sauvignon Blanc you can find from New Zealand and leave it open for 4 days!
Love Buzz from Anchorage, also a dry-hopped sour, is similarly citrusy. Damn, I wish I didn't have to trade to get more of that...
My favorite beer in the world. Hear the next batch is supposed to be released in April. Also, Anchorage and Jolly Pumpkin are releasing a collaboration beer soon called Boreal de Calabaza. It's a Saison brewed with Grapefruit peels and fermented with Brett.
I tasted a grapefruit saison at a beer event a few months ago. Do not remember the name but it was actually pretty good. Saw it at TW a few weeks ago.