I have a friend with blog that you should certainly check out. It's called Manly Project for Manly Men. In this post they make blackberry mead. Please check out the blog at http://manlyprojects.blogspot.ca
I Used To Be An Adventurer Like You...
As there's no mention of what is in Black-Briar's mead in game, this is a just-for-fun imagining of it. The Black-Briar crest features what appears to be a thorny vine with the leaves of a blackberry bush, so that's what I'm basing it on.
Fun fact: I almost horribly burned myself doing this in a fairly comical way. I'll get to that at the bottom of the tutorial