In terms of physics, I'd say this could happen when the pressure in the jar is just barely below the atmospheric air pressure. The weight of the atmosphere pressing down pops the lid in, and since the lids have some springiness built in, they pop to concave all at once. But that's a pretty good size change in volume, which could increase the pressure in the jar to just above atmospheric and pop the lid back up. It could fight back and forth until the falling temperature gets the internal pressure low enough to stay below atmospheric even when compressed by the concave lid.

In terms of canning, I've never seen this, just sometimes seen a lid ping if I took too long moving it to the pot, then unping when put in the water and reheated a little (while I'm still filling the other jars).

If they all sealed, you should be ok, as long as you didn't touch the lids while they were cooling. If you "helped" it seal, it might not really be sealed.

Melissa

No ma'am, I never touched them, never do!
Thanks!

June - you didn't say but did you remove the weight when it reached zero and then wait 10 mins. or had you left the weight in place?

Removing the weight at zero allows for a gradual equalization in pressures over that 10 min. wait period. I be sure to check the seal well on the one that pinged several times and I'd mark it and use it first. Sometimes that "belching" can deposit food on the jar rim and the seal fades over time. Otherwise I'm sure they are fine as Melissa said.

Dave

Digdirt...I REMOVED the weight after the pressure was zero, and waited another 10 minutes before opening the lid. I always set the timer again when I remove the weight, and wait again till I take them out, after I open the lid. Some things, like chicken stock, can still be boiling. It wasn't since it was salsa (I couldn't see it boiling, doesn't mean it wasn't a bit), but I still waited. Thanks for the tip though...I couldn't figure out which jar was doing it as a few of them were and it was hard to tell. It was almost comical in a way! I will double check all seals, believe me!
Ken. No fans nearby. I do have a ceiling fan in my kitchen. It's possible I had it on a higher speed. That may have caused it.

Thanks so much!

Okey doke. ;) You dun good.

Dave

PS: I need my ceiling fan running too when canning. Lifesaver!

I have been scouring the internet for an answer to this very question. I have canned for a number of years but only got into canning meats with a pressure canner for 2 years now. After Thanksgiving I decided to can turkey broth. I also followed Ball Book exactly. I had never experienced all that pinging before! I caught a sale on chicken quarters, canned the meat with no problem and then canned the broth with all that pinging again! Might it have something to do with canning liquids only? The seals are all good but are the contents safe? The only answer I found was one lady who said she leaves her broth sit in the canner for at least an hour after the pressure has fallen before she removes the lid and that solved her ping problem. I have not used any of my canned broth yet since I was searching for an answer as to whether or not it was safe. I will try leaving it sit for an hour the next time.

That repetitive pinging is totally normal. As your broth cools that pinging will stop.

If you followed current recommended time and procedures you have nothing to worry about.

Don't leave your broth in the canner the additional hour. It's unnecessary. Leaving jars in the canner too long can actually create the very food safety issues you're trying to avoid.

Carol

Thank you Carol! I called my county extension and they were baffled, had never heard of this before. I feel much better now. Thanks, Jan

The last two batches of broth (one beef and one chicken) did this too. I followed directions precisely and they both pinged and ponged till the cows came home. I've canned meat products for at least 20 years and this is also the first time it's ever happened to me. I didn't question safety, however, and when cooled just shelfed them. But you are not alone with this phenomenon and it's also a new one on me.

I'm no physicist and I didn't think of it before, but lids now are lighter and thinner, so that may be a factor.

Carol