I've been buying unpasteurized orange juice recently for its richer flavor, as compared to pasteurized OJ. I've had some sitting in the fridge for about a week, and upon tasting it just now I noticed an extra tang that I'm pretty sure was not there when I first bought it. I presume this is due to some new acid in the juice that has formed from the breakdown of other components of the juice as it aged. I quite like this additional complexity of the flavor, but I am curious: What is it? In particular, what acid might I be tasting?

  • 2
    Could it be alcohol? Jul 14, 2016 at 8:32
  • I had this happen just this week to unpasteurized OJ. We did not smell anything off, nor taste any bad or even alcoholic, but it tasted slightly carbonated to me. I vote CO2. From some kind of organism.
    – Lorel C.
    Apr 6, 2017 at 4:51

3 Answers 3


It is almost certainly a fermentation - opened juice does not keep for a week in the fridge. So you got some bacteria in it which are creating tangy byproducts (lactic or acetic acid). It is a method of creating fermented drinks such as cider (or even fruit wine), but without following a tested process, you cannot be sure if some of the bacteria may be harmful. So it is not safe by today's standards.

  • So do you think it's fermenting and will turn to Alcohol I've had old juice go bad on me and other juice I drank knowing it was old but never got drunk .I'm single so I buy in smaller quantity now .
    – user48092
    Jul 17, 2016 at 0:57
  • 1
    Fermentation does not automatically mean alcohol (sauerkraut is not alcoholic, for example) and when it does, it creates alcohol slowly. If yours was an alcoholic fermentation, you probably had 0.5% or less alcohol in the juice, you would have needed to drink 3.5 liters to feel the same effect as from one small beer.
    – rumtscho
    Jul 17, 2016 at 7:43

I just opened a jug of unpasteurized orange juice that had been sitting in my fridge for a couple of weeks (as long as I've ever let it sit) and got a huge wallop of what I'm pretty sure is vinegar. So I believe the acid in question is acetic acid.


What is it? In particular, what acid might I be tasting?

Could be all kinds of stuff. In any event, you can be almost certain that a changing flavor of unpasteurized OJ is due to something not very healthy. Example literature.

If you really like the acidic flavors, consider purchasing pasteurized OJ, and then adding Tart Cherry Juice Concentrate. Or even food grade citric acid, a common ingredient in Sherbets.

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