Go to Kazordoon. After you pass the part with the lava to enter the city, while you are in the part that has some Rats, go left instead of north, and follow the way up to the mountains.
On the last floor, on the right-bottom corner, there will be a Cask of Brown Ale. Fill the bottle with it and bring it back to Boozer to get your reward.
Player: hi Boozer: Welcome to the Hard Rock Racing Track, Player. Player: mission Boozer: Shush!! I don't want everybody to know what I am up to. Listen, things are not going too well, I need a new attraction. Do you want to help me? Player: yes Boozer: Good! Listen closely. Take this bottle and go to Kazordoon. I need a sample of their very special brown ale. You may find a cask in their brewery. Come back as soon as you got it. Player: bye Boozer: You'll be back.
Player: hi Boozer: Welcome to the Hard Rock Racing Track, Player. Player: mission Boozer: Yessss! Now I only need to build my own small brewery, figure out the secret recipe, duplicate the dwarvish brew and BANG I'll be back in business! Here take this as a reward.