Hmm... never had twisted tea - but a few thoughts:
1) Fermented "sweet tea" from McDonalds will probably taste nothing like twisted tea. It probably will be pretty nasty and a waste of good sweet tea! McD sweet team = yummy, but after its all fermented out I can't imagine it being good or tasting like tea...
2) I can almost guarantee twisted tea is artificially "tea" flavored and/or back-sweetened after fermentation.
3) No clue what they use to sweeten McD tea, but if they use artificial sweetener/sweetnlow/splenda type "sugar", etc. it may not even ferment. If they use normal sugar in that sweet tea, it takes A LOT of sugar b/c that tea is pretty darn sweet!
Maybe you can pull it off - but I think it will take some backsweetening and maybe some tea flavoring/powder afterwards to get it back to tasting like sweet, hard tea... Let us know how it turns out!
