Why did my canning jar break?

There is nothing more frustrating than taking the time to pick, prepare, and can something and open the canner to find broken jars and wasted food.  Here are the top 12 reasons your jar might break boiling water bath cannersinside the canner.

  1. Using old jars. Antique canning jars are attractive but perhaps not the best choice for a product that is very labor intensive to prepare.
  2. Nicks or small cracks in the jar. Always check for small nicks or hairline cracks before filling jars.
  3. Not releasing trapped air bubbles inside the jar.
  4. Using metal utensils to release trapped air—this can cause scratches or weak spots inside the jar.
  5. Overfilled jars.
  6. Fluctuating pressure inside a pressure canner. Watch the gauge or listen to the “jiggle” of the weight to maintain a constant pressure.
  7. Reducing pressure too quickly. Resist the impulse to run cold water over the pressure canner after the processing time is up. That is a quick and easy way to destroy all your hard work.
  8. Placing hot jars into a canner of cold water.
  9. Forgetting to add water to the pressure canner.
  10. Forgetting to put the rack into the bottom of the canner. Jars bouncing around during processing are at a high risk of breaking.
  11. Setting your hot, already processed jars into a draft to cool.
  12. Screwing the bands onto the jars too tightly. Remember, finger-tight only.

Following canning directions carefully will help you avoid jar breakage.

Liz Meimann

I received both my undergraduate and graduate degrees in Food Science at Iowa State University. I love to quilt, sew, cook, and bake. I spent many years gardening, canning, and preserving food for my family when my children were at home.

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6 thoughts on “Why did my canning jar break?

  1. I’m trying canning the second time and broke 3 0f my 4 jars as I introduced them into the pot of boiling water.any reason why this happens.
    I tempered jars to sanitize.
    I sanitized rind
    gs and new flat seals.
    I filled to 3/8 to 1/4 inch
    of space .
    the jars were filled with hot veg salsa, rims wiped, band and seal flats hand tightened. my have over tightened?
    ball measure stick to help remove air and check head space.
    the very minute I carefully set into the pot of boiling water ,they popped.all bottoms broke out.

    I successfully canned fruit jam two years ago no problem.
    used new and older recycled jars all ball or mason.
    the ones I used that broke were recycled ball but looked to be a thinner jar, they were bought at a local veg market containing elderberry suryp. are jars different types a

    that can’t take the boiling process?

  2. David, There is a possibility that the jars you used either were not tempered canning jars or they had small hairline cracks caused by metal. Since I do not know exactly what you were canning and the recipe used, I don’t know if the head space was appropriate. Over tightening the lids could also be the problem especially if there was a lot of air left in the jar. The temperature of the canner water should be about 180F when the filled jars are immersed into the water. Aside from the jars breaking, I hope that you were using a USDA approved recipe for whatever kind of salsa you were making. High acid salsas are appropriately processed in a hot water bath while others made with low-acid vegetables need to be processed in a pressure canner to be safe. Check out the National Center for Home Food Preservation for more information.

  3. I just had a quart jar of peaches break in two during the processing in my canning pot. I placed a ladle under the broken jar and managed to scoop out most of the peaches as I removed the jar. I noticed when a jar breaks, it usually is a clean break, no chips or splinters. Since I had plenty of syrup available, I rinse the peaches off, place them into another sterilized jar, added the syrup and canned these peaches. I’m not sure what I’ll do with this quart yet, has anyone else noticed these clean breaks with their mason jars?

  4. Hi, the clean break is quite common when it happens inside the canner. Even when a jar ‘explodes’ due to a tight ring, the break is clean rather than shattered. Most cracking is due to thermal shock or sudden expansion. Typically, jars that experience thermal shock crack cleanly at or near their base, all the way around the bottom of the jar leaving the base separate from the rest of the jar. This is due to uneven heating of the glass at the bottom-to-side transition zone. If there is a weakness in the jar, it is more likely to crack from thermal shock. One of the biggest causes of weakness in jars comes from the microscopic scrapes left in the glass from metal utensils. Thermal shock of jars seems to be more common with raw packed product. Cool jars loaded into boiling water are asked to expand rapidly.

  5. I got rid of my glass pyrex because of reports it can explode while empty in storage. Have glass mason jars exploded empty, stored?

  6. Hi Bonnie, Glass mason jars made for canning should not explode on the shelf whether full or empty. If jars break on the shelf, it is likely due to some kind of stress put on the jar prior to- or during canning or while in storage. Glass jars should not be used in an oven as they are not suitable for dry heat; explosion or breakage is a possibility.

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