Not much, as far as I can tell. I tried a porter and a black IPA side by side, and while the black IPA was a bit hoppier, it was only just a touch so, certainly not so much that I would necessarily be able to tell them apart in a blind taste test. Obviously, this is not an exhaustive study, but I have now tried enough to think that black IPAs are just a marketing tag and not much more. That does not mean they are not good beers. Some of them are excellent. I just don’t know that they deserve their own classification. I also recognize that no one else cares about this distinction, so I will shut up and get to the beers.
The Black IPA: I sampled the Sam Adams Dark Depths Baltic IPA. This poured a dark brown with a creamy cola like head. Roasted malts are immediately apparent in the aroma, along with some flowery and fruity hops. The flavor followed the aroma with the addition of some mild dark chocolate notes. I enjoyed this beer and tt is certainly a bit different from the standard brews from Sam Adams. Would I have another? Sure, with a grade of 6.5/10, I would definitely have it again. Would I say “no way can this be described as a porter”? Absolutely not.
The Porter: The always excellent Ska Brewing was represented by their Nefarious Ten Pin Imperial Porter. Pouring a an opaque black, with a hint of molasses in the aroma, along with some earthy hops, this had a creamy tan head which quickly dissipated. It had a mild coffee flavor and a noticeable alcohol warmth. The hops are less prominent than in the Dark Depths, but they are present, and become more prominent as the glass warms. This is an excellent porter, 7.5/10, and I’d give it the same grade if Ska called it a Black IPA.