By not drinking it?
This is not a difficult task, and I am somewhat practiced at it.
I have not yet acquired the palate discerning enough to distinguish the educated soft drink from the layman.
I'm very good with Coke though, I can distinguish by taste alone Coke from a can, Coke from a plastic bottle, and Coke from a glass bottle, and of course, Coke from those taps in restaurants, which tends to be far too sweet and more resembling of Pepsi.
Actually, I think that if I were to put effort into it I would be able to identify which Athens restaurant a random cup of tap-Coke originated from, but I feel that this would be of limited application.
Just like my degree
Snare, Crash cymbal.