Canning: Why Jars Break or Don't Seal
- Kelsey
- Aug 28, 2023
- 3 min read
Canning is definitely one of those parts of homestead living that can be tricky. Some batches are perfect, resulting in zero errors. Others can have several jars that break, don't seal, or lose water in the process. Here are some reasons why that may happen.
In this post:
Reusing Lids
Not only will this result in unsealed jars, but it puts you at higher risk for unsafe food. Canning lids have a special sealing compound around the rim and are designed for one time use when being used to process canned goods.
Defective Rings
While you cannot reuse canning lids, you CAN reuse the rings! However, if they are at all bent or warped in any way, it's probably a good idea to pass on those when it comes to preserving your food using a canning method. Also, make sure your ring is secure, but not too tight as air needs to be able to escape during the canning process.
Failure to Wipe Rim
It's so important to make sure to wipe the rim of the jar clean before adding and tightening a lid on. This is because food or other substances can become trapped between the jar rim and lid and can cause seal failure. To wipe, make sure you're using a clean, damp dish cloth or damp paper towel and simply go around the rim once.
A Nick or Crack on Rim
Before beginning your canning process, it is really important to fully inspect the jars for any cracks or nicks, not only on the rim, but over the whole jar from top to bottom. A nick on the rim is enough to cause a lid not to seal properly. To check your jar, simply run your finger around the rim of the jar and see if you catch on anything.
Not Following Instructions
Most canning instructions are similar, but it's a good idea to verify that the recipe or set of instructions you have chosen to follow are verified canning safe instructions. Failure to follow instructions exactly as written puts you at risk for jars not sealing or possibly breaking.
Too Much or Not Enough Jar Headspace
In most cases, there has to be a specific amount of headspace between the lid and the food inside of the jar, typically anywhere between 1/4-1 inch. It leaves room for the food to expand when heated and to achieve a proper vacuum seal. If you find you have a lot of headspace with not enough food to fill a jar, you can stick it in the fridge and use it first, or choose a smaller jar.
Wrong Temperature/Amount of Time
Processing at the wrong temperature or less time than instructed may prevent a proper vacuum seal from forming. Again, be sure you are following a verified recipe or set of instructions. You can usually find these in your canner instructions as well. Also, try to keep your jars somewhat hot enough that the transition from filling to the canner doesn't cool off too much. Sometimes simply going from being much cooler to boiling water is enough to break glass in a snap. (You'll hear a "pop" when you add your jar to the water pretty instantaneously!)
Old Mayo or Pasta Sauce Jars
You may be wondering if it's okay to use old commercial mayonnaise, pickle, or pasta sauce jars instead of actual jars made for canning like Ball or Kerr. The majority of our jars have been handed down to us, and a large number of them were not made to be used a second time in a canning situation.
But is it worth it to use them? The short answer is it depends. Most of the time they have worked for us, but these jars are more susceptible to start to breaking or not sealing. They are sometimes not made to withstand extreme temperatures like actual canning jars, and the lids are more susceptible to not sealing because they have a different sealing edge.
When it comes to canning, it's always better to err on the side of caution. However, all is not lost if your jar does not seal properly. In some cases, you can try and reprocess your jars. When we have situations where our jars don't seal, or we lose a certain amount of water in our green beans for example, we immediately refrigerate those and use them first. If you have a situation where a jar breaks in the canner, carefully remove the rest of the jars after processing and then dispose of all of the glass, lid, ring, and food contents.
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