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May 29, 2012 04:11 AM

Canning question--about headspace

I made some raspberry jam in 4-oz jars and I had some leftover, which inlaced in a clean jar in the fridge. One of the seals failed, so I decided to reprocess, in using the leftover bit in the freezer. Recooked the jam, placed into sterilized jars, and water bathed for the appropriate time. One of the jars had just over 1/2 inch headspace instead of 1/4 inch. If it had been a half-pint jar, I'd have no hesitation about storing at room temperature. Do I need to worry about a 4-oz jar? Btw, the seals are fineon the reprocessed batch.

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  1. If your reprocessed jar sealed, you should be fine. In my understanding, the headspace requirements are minimums, not maximums, in order to allow the contents of the jar to expand as necessary while being processed. Filling a jar only half full can be problematic for a number of reasons, but a quarter inch isn't going to make much of a difference.

    1 Reply
    1. re: JoanN

      Thanks, JoanN! Overfilling is what caused the seal failure in the first place.

    2. My understanding is that each process time is calibrated for a specific amount of head space. Too little headspace and product could bubble up and interfere with a proper seal.

      Too much headspace can cause problems too. The process time may not be long enough to remove the excess air resulting in a poor seal. Even if the seal is good, the excess air left behind can cause discoloration of the food.

      2 Replies
      1. re: meatn3

        Both true, meatn3, if you're only filling a jar, say, halfway. But neither will be a problem with only 1/4 inch of extra air. I've had jars of jam with an more than an inch of headspace that maintained both seal and color for at least a couple of years.

        1. re: JoanN

          Good to know. Canning brings out my obsessive side, so I have not experimented with head space! Always good learn from someones practical experience!