As with any problems when cooking, there are many reasons to answer a question. For pressure canning, here are some reasons for the question above:
- Improper headspace to allow for food expansion.
- Pressure canner was not exhausted for 10 minutes before pressurizing.
- Pressure too high.
- Unsteady heat source caused pressure fluctuation.
- Removing pressure regulator before pressure dropped completely.
- Rapid temperature changes or drafts blowing on the canner.
- Lids not applied correctly.
- Raw pack was used instead of hot pack.
- Did not leave canner closed for 10 minutes after pressure dropped completely.
Source: www.gopresto.com and https://nchfp.uga.edu/how/general/cannedfoodproblems.html
