Question About Cracked Jars

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Assistant Cook
Sep 17, 2022
So I'm brand new to canning. I've water bath canned a few batches of jam, and the other day I pressure canned 2 types of soup (together, because their processing requirements were the same). When I pressure canned the soup, 2 of the 7 jars cracked and were lost, the rest were fine. The curious thing (to me, anyway) is that the cracked jars were the only 2 jars of Chicken Pho (which had lime juice for flavor, so I don't know if acidity was a factor?) but ALL of the beef stew jars remained intact. So my question is: was this coincidence? They WERE both next to each other, if that matters. I've read that broken glass from one jar can crack other jars. I'm just curious, since all other conditions were fine for the other 5 jars, why did the only 2 jars with chicken pho break?

Any sort of heat-related element shouldn't apply, since I set the jars in the water before boiling, so they didn't rapidly go from cold to hot. Also both batches of soup were fresh and relatively hot anyway, as were the jars which had been in hot water before being filled. I guess I'm just curious about the coincidence of it specifically being the chicken soup containing lime that was affected. Any and all input from more experienced canners appreciated, thanks!
I can about 500-1000 jars a year, and I've never come across lime juice or acid causing problems with jars cracking.
Sometimes jars have hairline cracks I might not notice, which will crack. When I'm washing them I hold them up to the light and check the bottoms, and sometimes find cracks that way. I never keep them because I might overlook them later and use them for canning. My husband asks me, why is this jar in the recyclables? It's just cracked.

Mostly my jars don't crack but temperature differences are usually the cause, for me. If they are the first jars put in the canner, for me, it's temperature difference.
I had my first jar crack on me last year (first time in 20+ years) then another. It was in my pressure cooker, which I have only been using for the last 5 years. I only did water baths up till then.

Anyway, I realized I was tightening the bands too much. It says finger tighten and I was using a bit of my wrist when tightening. Since I have only used my fingers (sounds so funny) it hasn't happened again.
Finger tip tightening @sadie33 yep very important. My husband tries to help sometimes but he strong arms them overly tight, so we compromise, he sets the rings on them, and I do the tightening. I also use tattlers and I tighten them and then back them off 1/4 inch from fully tight. Later with tattlers, when they come out of the canners, he tightens them.

With overtightening the metal lids, they will buckle when sealing because there's not enough give in them.

Maybe with the cracking jars, they have imperceptible hairline cracks, and they are fine at boiling but then with the high pressure they finally give way and crack? I don't know otherwise.
Even though some glass jars will easily last 20 years or more - glass still "ages" so sometimes those invisible hairline cracks are like our faces - only show up with time o_O ;).
I have glass jars and the original lid no longer fits. I repurpose it for something else.
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