Tuesday, May 24, 2022

Canning Jars Not Sealing? Reasons for a False Seal and How to Reprocess Canning Jars

Canning lids didn't seal?  Learn about canning jars not sealing and how to reprocess canning jars safely if you notice the canning lid popped up.  There are several reasons for Ball canning lids not sealing, and we will learn what they are and the procedure for reprocessing canning jars.

Why Are My Canning Lids Not Sealing?

Canning is a labor of love.  Every year during canning month (August), I wonder why I do this to myself.

Then in the winter when I'm eating the fruits of my labor (literally), I remember why I do it.

Perhaps the most frustrating thing in canning is when you go to your jar stash and find that your canning lid popped up and the food spoiled.  

A false seal canning is a common problem along with how to fix runny jelly or jam.   But don't let these problems turn you off from canning your own food!

There are several reasons for new canning lids not sealing, and I'll discuss some common problems and how to fix them.

For canning recipes, check out these posts:

I recommend keeping a canning journal so you can save your favorite recipes and keep notes to use year after year.  

How Do Canning Jars Seal?

Before we discuss canning jars not sealing, let's learn about the magic that happens when you can food.  When you can food at home, you'll fill the jars with the food and place a metal lid and band on the jar.  Then place the jars in water and heat until boiling (or use a pressure canner).

As the jars heat up, the contents of the jar expands.  This changes the pressure inside the jar.  Gases (air) leaves the jar.  This makes the pressure outside of the jar greater than the pressure inside the jar.

As the jar cools, this difference in pressure pulls the lid down onto the jar and forms a vacuum seal.  This is what seals the jar and prevents food spoilage.  

Do canning jars seal as they cool?  Some jars will seal in the canner or as soon as you lift them out, but most seal after the jar has cooled a bit.

How Long Does it Take for Jars to Seal?

Canning jars can seal as soon as you take them out of the canner, but often they don't seal for a few hours.  It can take up to 24 hours for a jar to seal.

Be patient.  I know you're excited to see if your jars sealed, but let them sit overnight without touching them.  If you press down on the lid before it's ready, you can create a false seal canning.

What Happens if Lids Don't Pop When Canning?

If your lids don't pop right away, let the jars sit untouched for up to 24 hours.  It's important to let them rest while they cool, so make sure they are out of the way when you remove them from the canner.  

After 24 hours, then test them.  If they don't seal, then you can reprocess them.

What is a False Seal in Canning?

A false seal canning is when the proper steps were not taken for canning, which makes the lid appear to be stuck to the jar.  However, it did not create a vacuum that will seal the jar and prevent spoilage.  

How to Tell If Canning Jars Sealed

To test your jars to make sure you don't have a false seal canning, let the jars cool completely for at least 24 hours.  Then use your finger to press in the middle of the lid.  If you can push the center down and it pops back up, the lid is not sealed properly.

You can also tap the lid with the bottom of a metal spoon.  If it makes a dull sound when you tap it, the lid isn't sealed properly.  It should make a high pitched sound.  

You can also look straight across the jar at eye level.  The lid should be curved down slightly in the center.  If it's flat or curved up, then the lid is not sealed.

Can You Reprocess Jars That Don't Seal?

Yes, you can reprocess the food if you find canning lids not sealing or your canning lid popped up.  Remove the lid and ring and inspect the top of the jar to ensure there are no nicks or chips in the jar.

Then inspect the lid to make sure it has a good seal.  If the lid looks good, you can reuse it.  However, if several lids failed, then I will usually get new lids.

You can also place the jar in the fridge and use within a few days or freeze the contents of the jar.  If just one canning lid popped up, then I usually just use it right away or freeze it and don't bother reprocessing canning jars.

Why Did My Mason Jars Not Seal?

There are several reasons for canning jars not sealing.  Let's look at some possible reasons why canning lids will not seal so you can determine what happened before reprocessing canning jars.

Not Using the Right Jars

For best results, use jars made just for canning.  Brands include Ball, Golden Harvest, or Kerr.  There are other brands, but I like to stick with Ball or Golden Harvest.

You  might be tempted to reuse mayo or other jars.  I don't recommend this because the glass may not be able to withstand being heated several times.

Furthermore, the lip of the rim may be too narrow or the wrong size to get a good seal with a canning lid.  

Chipped Jars

Visually inspect your jars before adding the food.  Look for small chips or cracks.  These can prevent a good seal.  

I recommend looking at the jars and running your finger around the jar.  Sometimes there's a small crack that you can't see, but you can feel the nick.

Rim of Jar Not Clean

It's important to wipe the rim of the jar clean after you fill it but before placing the lid and ring on top.  I use either a damp cloth or vinegar to wipe the rim of the jar.  

If there's food on the rim of the jar, it can prevent a good seal.

I use a push down bottle filled with vinegar.  Then I can quickly press down with a dish cloth and wipe the ripe.


Make sure your rings are not bent or have rust on the inside of them.  Once they get rusty, it's time to use them for crafts like canning ring coasters or a canning ring wreath.

You also want to ensure that the rings are tightened properly.  Turn them fingertip tight.  I know that's not precise, but it means tighten with two fingers holding the band.  Don't use force to tighten them.

If they are too loose, it can't create a seal.  If they are too tight, air can't escape during the heating process.

Preparing Lids

You do need to boil your jars and rings before canning, but don't boil the lids.  Wash them and rinse them.  Then place them in hot water (but not in boiling water).  

Back in the day, the lids needed to be boiled.  Today's lids have a thinner coating, so they don't need to be softened by boiling.

In fact, if you boil the lids, it can soften the coating too much, which can create a false seal.  You'll store the jar thinking it's sealed, but you'll often find the canning lid popped up after storing it.

This is another reason I never store my canned food with the ring on it.


Each canning recipe will say how much headspace to use.  You can check the headspace using a bubble popper and measurer.  (This is on my list of canning supplies for beginners, and I highly recommend using one.)

Too much or too little headspace can prevent jars from sealing.  Learn more about canning mistakes that can kill you for safe canning.

Not Enough Heat

It's very important to process your jars in the correct method (water bath or pressure canner) for the directed amount of time.  

This ensures that the contents of the jars get hot enough to kill bacteria and germs, and it also helps create a vacuum.  

By the same token, only use safe and approved canning methods.  You may experience more sealing failures if you use open kettle canning, oven canning, or inversion canning.

Not Removing Air Bubbles

Air can get trapped in the jar when you fill it.  Use the bubble popper to remove air bubbles.  

Trapped air can increase the amount of headspace in the jar, which can make your jars not seal properly.

Once your jars are cooled and sealed, remove the rings and move the jars to storage.  If your jars sealed right away, then they will usually stay sealed.  

Every once in a while I find a jar that didn't seal or the canning lid popped up during storage.  If that happens, toss the contents of the jar and the jar itself if you suspect botulism.  

I've seen a lot of Ball canning lids not sealing since the events of 2020.  The lids are thinner now, and the quality just isn't there.  

Even before that, I'd had a few random bad boxes.  It's frustrating when you spend all that time canning and have to spend more time reprocessing canning jars!

I buy my lids in bulk from the Amish bulk food stores now.  I wish I had a link to share, but no English have posted them online yet.

Now you know what causes a false seal canning and how to reprocess canning jars!

Like this post?  Pin it!

No comments:

Post a Comment