Strange Brew is related to the seasonal event Brewfest. Completing this achievement is also an objective of the meta achievement .
These beers can be purchased by <Voodoo Brew Vendor>, <Gordok Brew Vendor>, and <Drohn's Distillery Brew Vendor> during Brewfest. You can also get some of these brews from completing [1-70] . Note that they only last 2 days, and will then be removed from your inventory. However they are not BoP, and will not be removed if you mail them to an alt and keep them in your mailbox.