Why are My Canning Lids Not Sealing?

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Why are your canning lids not sealing? This is the fourth in a series of videos relating to possible reasons why your jars are not sealing. So far we’ve covered issues with a

  • lack of patience or just plain needless worry.
  • issues with your lids.
  • issues with your canning jars.

This post includes the possibility of issues with your canning methods.

Why are Canning Lids Not Sealing

Improper Processing

Processing your jars for the correct time and pressure causes the jars to “vent” properly. This means it expels oxygen out of the jar and contents. If the jar doesn’t vent properly, the vacuum seal won’t happen when the jar cools at the end of the process.  

Jars in the canner with water droplets on top of some of the lids.

Incorrect Headspace 

Headspace is important. This is the space between the food and the lid, usually 1/4” to 1” inch depending on the food you are working with. There is a reason there is a difference in headspace between different types of food.  What happens is as the food expands as it processes, oxygen is expelled from the jar and the food itself. Then the food contracts as it cools and the lids are pulled down to cause the seal. You need the correct amount of  headspace to allow that to happen.  If there is not enough headspace the food itself will push out through the lid and may end up blocking that seal. It won’t always cause an issue, but occasionally it will.  

Ruler standing upright next to a glass canning jar to measure headspace.

Cooling Your Canner Too Quickly

If you rush the process of cooling your canner and jars down too quickly, it can cause liquid loss.  It can also cause food to be expelled from the jar, and just like with incorrect headspace, food may block the seal.  

Tightening the Screw Bands Too Tightly

When you place your lids on the jars, you need to tighten the lids just “finger tight”.  You do not want to really screw that band down hard. Remember, the jar needs to vent. The problem with this is usually a crimped or buckled lid, which will still sometimes seal. But that seal may be weak, as where the crimp is, the seal may be compromised.  

Okay, how can I explain finger tight? It can be subjective, so don’t overthink it. I just tighten the bands down as if I’m putting the jar in a fridge and I want to be able to get the lid off later. If you have really strong hands and tend to over-tighten things in your fridge? Be aware of that. Is your family always bringing you jars to open because they can’t do it? That is too tight.  🙂  

I often put my finger in the middle of the lid, then use my other hand to screw the band down.  When the jar turns on the counter…it is tight enough.  

Here’s a link to more on tightening lids.

Sharon tightening the ring on a jar filled with peppers.

“Why are My Canning Lids Not Sealing?”

Don’t be overwhelmed by this list!  These are all possibilities of why your lids didn’t seal, but it is likely not all of them. Watch the rims and the quality of the seals. Those are the two most likely reasons. If there are no issues there, then you can look at the other reasons as well.  

Links to the rest of the series.

  1. What Causes Jars to Not Seal: 10 Common Reasons
  2. Why are My Canning Jars Not Sealing? Canning Jar Issues
  3. Are Canning Lids Supposed to Pop? Why are My Canning Lids Not Sealing?
  4. Why are My Canning Lids Not Sealing? Issues with your canning methods. <– you are here.

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Colorful jars of home canned food, including citrus fruits and beets.

What Causes Jars to Not Seal: 10 Common Reasons

What causes jars to not seal? It’s frustrating when you realize a jar didn’t seal properly. This series is all about figuring out what might be the problem.

Sharon holding a canning jar.

Why are my canning jars not sealing? Canning Jar issues

Ever asked yourself, “Why are my canning jars not sealing?” One possibility is that you have issues with your canning jars.

Sharon holding wide mouth and regular mouth flat lids.

Are canning lids supposed to pop?

So are canning lids supposed to pop? Is the jar sealed, even if you didn’t hear that ping? Here’s what you should know.

Page last updated: 2/18/2021

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Chris Benson
Chris Benson
2 years ago

First off, clean the top of the rim of the unchipped jar.

Rachel Abernathy
Rachel Abernathy
2 years ago
Reply to  Chris Benson

Yes, that’s right. 🙂 Sharon discusses the jars more on this page: https://www.simplycanning.com/why-are-my-canning-jars-not-sealing/

-Rachel (Sharon’s assistant)