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I've canned my whole life (54 years old), I started when I was young helping my Mom, and I've never run into this before.

I've never canned just plain pork stock before, but wanted to try. I had 4 pints and put it in the pressure cooker at 10lbs for 25 minutes. The book called for 11 lbs for 20 minutes.

When I took them out they started popping right away...but they kept popping several times. In and out of seal. Now they have settled on sealed "popped down".

Has anyone else ever had this happen, do they know what the issue was and they should be ok, shouldn't they, as long as they are sealed?

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See also: cooking.stackexchange.com/questions/36368/… –  Jefromi Nov 27 '13 at 18:35

2 Answers 2

This happened to me the other night. This is the first time I noticed the lids popping up and down for a couple of minutes after being taken out of the pressure canner. I was processing chicken broth. The only two anomalies were that I had taken the jars out relatively soon after the pressure allowed (instead of letting them cool longer in the canner), and I accidentally let the pressure rise to 15 lbs before I was able to lower it to 10. 25 out of 26 jars ended up with a proper seal once fully cooled.

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I waffled about whether this really answered the question, but I decided that since you did give two possible things that could cause this - early removal and too high pressure - it's at least an attempt. I'm not sure those are really the reasons though - it's just as plausible that you ran into any one of the more common problems. Imperfections in jars or lids, accidentally too short processing time, etc etc. –  Jefromi Nov 27 '13 at 18:25
    
For more, see cooking.stackexchange.com/questions/36368/… –  Jefromi Nov 27 '13 at 18:36

It sounds to me like the seal on the lids may be very slightly compromised. For example:

  • lids start down with a good seal
  • pressure can't escape and starts building up like usual
  • imperfection in lid seal gives way a vents out pressure/heat, lid pops up
  • jar/contents starts to cool, constricting, again like usual - this is what seals the jars in a normal procdure
  • Lather, rinse, repeat

Edit

A thought occurs: it's equally as likely, if not more so, that the opposite of what I described above is happening: i.e., the stock is cooling down and contracting, which creates a negative pressure on the jar, sealing it. However, in a similar fashion to the above, a slight imperfection in the seal holds to a certain level of pressure but gives way past that threshold, allowing the pressure to equalize (which causes the top to pop up).

If they settled in the lid-down position after they completely cooled, they are probably okay (note the probably). What causes a lid to 'pop' after it cools is usually due to bacteria being sealed inside the can and/or compromising that can afterwards. Bacteria starts to eat the food, produces gas which expands and POP goes the lid, and your delicious canned food is no longer safe to eat. So if the lids stay down until you open the jar and the stock still smells okay, you're probably safe.

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