Blackrock Lager is the June brew from the Brew of the Month Club.
All members of the Club get free sample of the brew in their in-game mail at start of June. Should you want more, your local Brew of the Month Club Brew Vendor sells it in stacks of six till the end of June.
Like any weak alcohol, this makes you slightly drunk. Also, like all Brew of the Month brews, drinking one of these will create a Empty Brew Bottle that can be targeted and thrown.
Special effect of this brew is chance to get "Internal Combustion: That last bit of brew is burning up your insides!" buff for 5 minutes, causing you to breathe red smoke, and removing the buff causes a massive burst of fire.