Been canning and messing with glass jars for close to 20 years, and this question pops up every winter. The short version: filling a hot jar with boiling water before dunking it in an ice bath is not a magic shield. What actually kills jars is the temperture difference between the outer surface and the inner surface of the glass at the same moment. Soda lime glass only tolerates a modest swing before the stress wins, and it doesn't care much wether there's water sitting inside or not. Here's what actually matters. Warm the glass up gradually instead of dumping boiling liquid into a jar straight off the shelf. A jar allready close to the temp of what's going into it has very little stress built up in the walls. Same logic in reverse: never rinse a jar from the freezer under hot tap water, and set hot jars on a dry towel instead of a cold countertop. A damp spot under a hot jar is a classic crack trigger, since the water pulls heat out of one little patch way faster than the rest of the base cools. Also keep in mind that not all jars are equal. Proper canning jars are thicker and more uniform than a recycled pasta sauce jar, and tempered glass shrugs off swings that regular annealed glass won't. One jar surviving an ice plunge just means that jar got lucky that day. Glass has surface flaws you can't see, and the same jar that handled it once can let go on the second try.
Tips for keeping glass jars from cracking when temps swing fast
Oct 27, 2026
Last reply: 23 hours ago
3 Replies
I ran my own version of this test a couple winters ago with a batch of turkey stock. Had six jars cooling on the counter and got impatient, figured I'd see how they handled a quick dip in a sink of ice water. Two of the six cracked, and the wierd part was it wasn't instant. One let go about ten seconds after it came out of the water, just a soft click and a hairline running down the side. That's when I stopped treating survival as proof of anything.
These days I just keep the jars in a warm oven around 200 for twenty minutes before filling. No cracks since I started doing that, and I go through forty or fifty jars a season between stock, chili, and apple butter. The oven trick costs me nothing and skips the whole gamble. One thing I noticed that backs up the damp spot issue. I used to cool jars on my laminate counter and had way more failures than after I started using a folded bath towel on a wire rack. Never lost one since the switch, and that was before I knew the reason why. My mother-in-law swears her jars are tough becasue she's never broken one, but she also never puts them through anything. She hand washes in warm water and shelves them. That's the real answer, honestly. The jars that last are the ones never asked to survive anything in the first place.
Agree with the bit about pre-warming the glass, that's been my expirience too. I fill mine straight from a hot dishwasher cycle and haven't cracked one in years. Before that I was pulling them from the pantry shelf and pouring soup into room temp jars, lost three in one batch of salsa. The difference was night and day just from the jar starting out warm. Also the delayed cracking thing is real, had one split open on the shelf a few minutes after canning, which is exactly why I stopped trusting a jar just because it made it through the bath.
The fridge is another one that gets people. I used to move a hot jar of sauce right into the fridge to speed things up and cracked two that way before I figured it out. Now everythign sits out on a cutting board untill it's barely warm to the touch, then goes in. Slower but I haven't lost one since. Also picked up the habit of tapping the jar lightly with a knuckle when I'm paranoid about a jar, a dull thud seems fine and a higher pitched ping ussually means something's already started. Not scientific but it's caught a couple before they let go on the shelf.
Join the Discussion
Have something to add? Share your thoughts — no account required.
Didn't find your answer?
Ask the community — no account required