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Why do jars crack sometimes?

Posted by n1st (My Page) on
Mon, Aug 16, 10 at 19:17

I was making dilly cabbage and while the water bath was boiling, I poured the near-boiling solution into the jars of cabbage. I took my time to clean the jars, add extra cabbage, top off the jars, etc. About 10 minutes elapsed before I put the jars slowly into the boiling bath. When I did, the bottoms cracked and fell off into the bath. I would guess there was a temperature difference of 212 vs. 175 between the bath and the soultion. Why did the canning jars crack? Now I'm weary of putting any temp jar into a boiling canner or bath. What is a safe differnce in temp?

Follow-Up Postings:

RE: Why do jars crack sometimes?

The water was already boiling in the BWB? Instructions say to heat the water in the canner to 140 degrees for hot pack and 180 degrees for cold pack. If it was already boiling then it needed to be turned off and let the temperature drop in it quite a bit or you get thermal shock and the bottoms fall out of the jars.

Were the jars already hot before filling them with the hot food? If not they need to be.


PS: Curious - where on earth did you find a recipe for Dilly Cabbage? Never heard of it before.

Here is a link that might be useful: NCHFP - How To Use BWB Canners Step by Step

RE: Why do jars crack sometimes?


Yes it was boiling in the bwb. I read the article at the link you provided. Assuming I put near boiling hot pack jars into a 180 bath that would allow for a 32 degree delta. My delta was about the same. Hmmm.

The Ball book says, for a pressure canner, to get the water to 180 before putting jars in it, and doesn't really distinguish between putting raw or hot pack jars into it, that I can see.

For Dilly Cabbage, I just use the Dilly Bean recipe...

RE: Why do jars crack sometimes?

I'll let someone else address the Dilly Cabbage issue.

When the bottom drops out of a jar, it's thermal shock. If it cracks vertically like a lightning bolt it's a stress fracture caused by previous damage which weakened the glass. Examples would be jars hitting against each other when being transported or scratches in the glass like damage from a metal implement when air bubbles are removed.

Breakage can also result from re-using commercial jars not designed for canning, using old jars which have accumulated scars or not using a rack on the bottom of the canner.

In this case, it's important to pack each jar, apply lids and put it in the canner rather than leaving it on the counter until all jars are filled.


RE: Why do jars crack sometimes?

Like Carol I'll pass on dilly cabbage issue except to say I'd be real concerned about such a short processing time for such a dense food - much more dense than beans.

But just adding near boiling liquid to jars, even hot jars, doesn't mean that is the temperature of the jar itself - the heat from the liquid isn't transferred to the glass that quickly - and that is why it breaks when it is a thermal shock break.

I am surprised that website says Make sure your canner is really boiling hard before placing your jars into it. They will slow the boil. since the time it takes to bring the water up to a boil is factored in when the stated processing time is computed.


RE: Why do jars crack sometimes?

What Causes Jars To Break?
There are several types of breaks that occur. Each break looks different and has specific causes. Thermal shock is characterized by a crack running around the base of the lower part of the jar, sometimes extending up the side. To prevent thermal breakage:

Avoid sudden temperature changes, such as putting hot food in a cold jar, putting a cold jar in hot water, or placing a hot jar on a cool or wet surface. Keep jars in hot water until filled.
Use a rack in the canner.
Avoid using metal knives or spatulas to remove air bubbles or steel wool pads to clean jars.
Internal pressure break is characterized by the origin of the break on the side. It is in the form of a vertical crack that divides and forks into two fissures. To prevent pressure breaks:
Provide adequate headspace in jars for food to expand when heated.
Keep heat steady during processing.
Avoid reducing canner pressure under running water or lifting the pressure control or petcock before pressure drops to zero.
Impact breaks originate at the point of impact and fissures radiate from the point of contact. To prevent impact breaks:
Handle jars carefully. Jars that have been dropped, hit, or bumped are susceptible to breakage. Test new jars that may have been mishandled (to see if they break) by immersing them in room-temperature water, bring to a boil, and boil 15 minutes.
Avoid the use of metal tools to remove air bubbles.
Avoid using old jars. Jars have a life expectancy of about 10 years.

RE: Why do jars crack sometimes?

This is so helpful. Thanks!


RE: Why do jars crack sometimes?

Thanks for all the feedback. Now that I've had this problem, I'll be more careful about keeping the liquids inside and outside the jar at a very similar temperatures.

Regardng the Dilly Cabbage, I agree. I found a recipe for pickled cabage, and it used 100% vinager vs. a 50/50 mix w/water, and the boil time was 20 mins instead of 10.

RE: Why do jars crack sometimes?

I agree, the cabbage should be all vinegar, not water added.

RE: Why do jars crack sometimes?

Thanks to everyone who contributed to answering this question Now I know how to avoid this problem in the future.

RE: Why do jars crack sometimes?

I went through a lot of effort once to roast sweet peppers to pickle. One of my lovely jars broke in the BWB. Very disappointing since there was only two jars to begin with!

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