Like most things, I don't know a lot about brewing, but I think it basically involves putting some sort of vegetable matter in water, adding yeast, and then waiting for it to ferment and become alcoholic (which is the main point, otherwise you'd just drink the water, right?). So...Is it even possible to brew blood? I don't think it is, at least in the way I interpret the spirit of the OPs suggestion to be.
Here's a report from someone who experimented with blood in their brewing process
http://manchesterhomebrew.co.uk/brewing-with-blood/ But this isn't just blood added to water with yeast to make "blood alcohol". It's adding blood to the otherwise normal beer making process to achieve a blood flavour of some degree. It's like the difference between adding blood to dough to make "blood bread" or trying to actually knead blood into dough and then baking that into "blood bread". Brewing with blood denatures the blood, so it'd be a stretch to call the resultant liquid blood-alcohol even if there was enough sugar in it to ferment properly.
If the problem is vampires suffer alcohol withdrawal because they don't drink alcohol, I think the best solution is to make vampires not suffer from alcohol withdrawal (and they can still drink or pretend to drink regular alcohol if they're trying to keep up a facade). Blood brewing if implemented (because it sounds cool?) would be some sort of magical alchemical process, I'd imagine. Also, I'd be willing to bet that the blood barrels you get from caravans are a bug that will disappear eventually when Tarn gets around to it, probably at the same time that they stop magically supplying fresh meat over miles and all the other caravan oddities.