About three weeks ago, I brewed iced coffee in a clean jar; I didn't drink all of it and left it in the refrigerator.

About 1/2 the jar was filled, I then traveled and when I came back, I found in the bottom of the jar something sticky like rubber.

Is this Kombucha ?

I didn't use any kind of "scoby" aka starter, it's just ground coffee with cold water and sugar. This isn't the first time this happened. It smells just as coffee would, nothing bad.

  • by the way guys.... this rubbery think doesn't float on the top it remains with the ground coffee down the jar, thanks
    – aLcOmAnDa
    May 4, 2015 at 22:11
  • How long were you away?
    – Tim Post
    May 5, 2015 at 5:43
  • Plus one for introducing the idea to me, stimulating a quick Google search. As Tim's explains in more detail, this doesn't sound like what Kombucha recipes would produce.
    – hardmath
    May 5, 2015 at 13:14
  • i've been away for 3 weeks and the coffee was in the fridge
    – aLcOmAnDa
    May 5, 2015 at 17:14

1 Answer 1


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 :)

  • I disagree with the assertion that you need a starter to brew fermented beverages; wine is often brewed with only the natural yeast from the environment for example. Scobys do grow in the refrigerator, just much more slowly than room temperature.
    – sig_seg_v
    Jan 21, 2016 at 21:54

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