What does it mean when the jar pops before pressure canning?
closed as unclear what you're asking by Erica, Ward, Debbie M., Catija♦, Stephie♦ Aug 5 '17 at 20:44
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Before they are sealed, canning lids pop. That is, the raised button in the middle of the lid can be depressed.
Sealing the lids involves heating the contents of the bottle which, when it cools, creates a vacuum that sucks the lids in. That vacuum is entirely responsible for the seal that keeps canning lids on. If the seal is broken or failed to form the lid won't be sucked down and will pop.
(Before consuming bottled food always check the seal to make sure the food inside was properly preserved.)
Pressure canning, besides sterilizing the contents of the jar, is also responsible for sealing the jars. There is no reason to expect the jars to be sealed before this step. In fact, the jars won't seal until they have cooled down after the pressure canning. My favorite part of canning is when the jars are all set out to cool and the lids start loudly popping as the vacuum forms and suck the lids down.
If after pressure canning the lids still pop then they failed to seal and that is a new question. Dlb commented above on reasons that might happen.