title_body: Is this coffee Kombucha?
upvoted_answer: In order to be Kombucha, you would need to have a starter, unless (somehow) enough bacteria was present in the coffee / sugar / cup (highly unlikely). It would also be extremely unlikely that even if a culture was unwittingly introduced, that it would bloom in cold water. It's not Kombucha unless it's actually fermented, and for that, you need a live, active thriving culture (you must have a starter).
  
  What you've probably got at the bottom of the cup is a combination of settled sugars and residual grounds. While I doubt that tasting it would be harmful, I wouldn't quite recommend it :)