I opened a jar of roasted peppers I canned about a month ago. Because it was a big jar and it ended up lacking water I put it in my 4C° fridge. It was canned at about 120C°-125C° without any additives like salt or vinegar.

After opening it, unlike other jars I've opened, I noticed a very subtle acidic taste, kind of like it was carbonated. It wasn't unpleasant and there is no bad taste or odor.

Is the jar spoiled or is this probably part of the normal range of flavors? Since paprika are very alkaline, why would it suddenly taste a bit acidic?

  • 1
    I can't tell you about the taste, but paprika are not very alkaline. They are very slightly acidic, like practically all fruit and vegetables.
    – rumtscho
    Commented Jan 2, 2020 at 22:42
  • "carbonated" usually isn't a good thing in canning. If something is actually creating gas, it might indicate fermentation or botulism. Assuming you used a Ball/Mason style jar with a dome lid, was the lid still vacuum sealed, or had it "popped up" or even been pressurised?
    – AMtwo
    Commented Jan 2, 2020 at 23:19
  • Hm now I reopened the jar and there was clear pressure and I now see bubble formation, kind of like a carbonated drink. So its most likely fermenting? Is it eatable or should I rather toss it? I had it in the fridge at 4C° so I guess it can't be botulism right? Commented Jan 3, 2020 at 0:05
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    @user1721135 your "it can't be botulism" statement is based on the assumption that the whole process went as planned. The fact that it is fermenting means that there were deviations between what you thought the conditions were, and what they really were - and you can't know what these deviations were, exactly. So at that point, anything is possible, you can't continue using your assumptions.
    – rumtscho
    Commented Jan 3, 2020 at 10:18
  • I just assume that the dangerous kind of botulism can not grow at 4C. Is this wrong? Anyway I tossed it, whatever it was it was not planned. Commented Jan 3, 2020 at 17:54

1 Answer 1


It sounds like (benign, tasty) lactic acid bacteria fermentation, possibly along with leuconostoc or something. But without the appropriate levels of salt, it's also possible that less friendly microorganisms are also growing.

As a rule, canned food with unexpected microbial activity -- regardless of process -- should always be discarded. Even if it's not botulinum (it's almost certainly not), a jar of peppers isn't worth a week on the toilet.

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