Testing Jar Seals And Reprocessing Jars (Safe Home Canning)

by Merissa on July 22, 2013

in Canning and Preserving

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I think that this is the part that most people panic about when it comes to canning. Did my jars seal? Are they safe for my family to eat? How can I be sure?

The scary thing is that the worst problem that can come from canning (botulism) is unable to been seen or smelled. So what can we do about it?

First of all, and this is the biggest thing...make sure you following the canning directions to the T. Make sure that you boil or cook your canned foods for the correct amount of time and the correct amount of pressure (if you are pressure canning). Make sure that during the time of cooking that your canner stays up to the correct pressure (or keeps boiling if you are water bathing) for the entire time you are processing.

You also want to make sure that you talk to your local extension office and find out if you need to make time/temp/pressure adjustments for your altitude. If you aren't familiar with your local extension office you can locate one here: US Extension Offices. (By the way, if you didn't already know, your extension office is a plethora of information on all things local, outdoors, growing food, ect. Utilize them!)

Once you have the cooking part down you shouldn't have much to worry about. But do you know how to properly test a seal on a jar? Here are some things to look for...


The most common method for testing jars is the Finger Test Method. Simply press on the middle of the jar lid with your finger. If the lid "pops" up and down with your finger when you press, it's not sealed and needs to be reprocessed. If it doesn't move at all it's sealed.

Note: Don't test canned foods until they are completely cooled and you've given them several hours to seal! Doing so might create a false seal and unsafe food.


The next method you can try is the Spoon Test Method. Tap the lid with the bottom of a spoon. If it makes a dull sound the lid is not sealed. If it makes a pinging noise it is correctly sealed. Please note that if you did not leave headspace and food is touching the lid it will create a dull sound either way.


Of course you can also look at the lid at eye level. If the lid looks flat or bulging it's not sealed. If the lid is nice and concave it's properly sealed!

My jar didn't seal...now what?

If your jar didn't seal don't stress and get upset. It happens to the best of us! Even experienced canners that have been canning for decades have jars that don't seal on occasion. If you have an unsealed jar or two, here's what to do.

Remove the lid and rim. Check the rim of the jar for any nicks or cracks. If you have a nick, discard the jar (or use it for dry food storage!) and place your prepared foods in a new, clean jar. Place a new lid on the jar and secure it with a clean rim. (Do not reuse the lid you already processed the jar with.) Reprocess the jar using the same process that you already used. It's a good idea to leave some time in between your canning so if unsealed jars do happen you can just add them to another batch instead of having just a single jar to re-can.

If you don't want to re-process your un-sealed jar you can always stick the food in the fridge or eat it for supper. Or you can just freeze the contents for future use.

How long have you been canning? Do you make sure to follow safe home canning methods?


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{ 17 comments… read them below or add one }

1 RevAllyson July 22, 2013 at 2:06 pm

We’re really careful to follow safe canning procedures when we do anything. :) New lids, clean rings, sterile jars, processing times checked, etc. I’ve never had a problem with bad food, although I’ve had plenty of seals fail for a variety of reasons. The exploding jar of spaghetti sauce was the worst, but at least it was contained in the pressure canner LOL…


2 Colleen July 23, 2013 at 6:28 am

I have a large family to feed, so we can on a large basis. About 300-600 jars per year. Safe canning methods are a huge part of our season. Not only checking lids, rings, and jars, but also making sure the canner seals are good.


3 happy momma July 23, 2013 at 8:32 am

I have been canning for a while. I have only had a few problems. We did have some salsa that became unsealed after about 6 months. It was the strangest thing. I am not sure what happened but I had about 15 jars that all of a sudden decided that they did not want to be sealed anymore. It was very sad to throw them all out. But then I had jars ready to be filled up with something else.

When I open up a jar I always ensure that the seal is still intact and I usually listen closely when I open it up. If I am in doubt, I will throw it out. I am not afraid to “waste” food if I am not sure of its quality even when It makes me sad. I try hard to ensure that it is good food for the family.

I know some people have had real trouble with the reusable canning lids. It is hard to tell if they are sealed, you don’t get that concave look, nor the sounds. They seem to have about a 50% failure rate. Many times you will unseal them trying to see if they are sealed. They seem to be a pain to use. I would not recommend them. Just stick with the old tried and true canning lids is what I think.


4 Merissa July 23, 2013 at 8:33 am

I agree, regular canning lids seem much easier to use and now that they are taking the BPA out of them I’m more than happy to keep using them!


5 Sue in Oregon July 26, 2013 at 4:05 pm

Merrisa, I am a 70 year old wife, mother and grandmother. I find your blog so refreshing and encouraging and just want to say “ThankYou” for the courage and knowledge you are sharing with others. I have been canning for years and get some strange looks when talking about ‘putting food up’ and canning. My mother-in-law gave me my lessons when I moved to Oregon and I have thanked her each time I pop the seal on a jar for teaching me a craft that has provided food for my family during some pretty lean times.
I have learned to take advantage of fantastic meat sales to can and have on hand for several years. Abundance in fruit and vegetables gardens of friends brings out the water bath canners/pressure canners and on food is on the shelf for future use.
I encourage men and women to learn how to can. Go to a senior center and talk with canners. Check out Extension Services at your local college for canning classes and teaching brochures. Your advice to follow directions “EXACTLY” in the Ball Canning Bible is right on. YouTube is also a great visual lesson for new ideas. Again, just like me tell you that I think what you share with others is a great service and very interesting. As my grand daughter would say……You Go Girl!”


6 Merissa July 26, 2013 at 4:06 pm

Thanks for all the advice and encouragement Sue!


7 Kim September 21, 2013 at 2:11 pm

I pressure canned peaches. I had some difficulty with the canning process (all the ater boiled away)> the jars all sealed. as long as the jars are sealed is the food safe to eat?


8 Merissa September 21, 2013 at 2:12 pm

Did you boil the water for the correct amount of time? If not, even though they look sealed they may not be safe and you might want to stick them in the fridge and use them.


9 Carolyn in Michigan September 28, 2013 at 2:34 pm

I used to can a LOT. But haven’t now for quite a long time. I recently was given a bunch of extra produce and decided to “put up” some of it. If I have to reprocess any of it, do I need to empty, clean and refill the jars…or just switch out the lids and put them in the water bath? Thanks!


10 Merissa September 28, 2013 at 2:56 pm

I don’t empty the jars, I just remove the lid and rim, then clean off the rim of the jar, replace it with a new lid and then reprocess.


11 Beth February 25, 2014 at 4:38 am

Great topic. As a relatively new canner (2 seasons) safety is a major concern. We always follow the directions very carefully and attend carefully when opening the jars. I have two questions for all of you experienced canners out there that will ease my mind greatly.

1) We check for head space when canning, but often it changes after processing. Is this OK? If we had 1/2 inch head space to start and the food moves around or shrinks, is the food still safe?
2) When we open, I like to hear a loud “pop” to know that the seal was intact. But sometimes we perform the above tests with success, open the jar, hear the suction/seal sound, but not the “pop.” Is this food safe, or do we need that loud pop?

We tossed 3/4 of our tomatoes because I didn’t hear the pop, but they seemed OK and I felt sure I was doing the wrong thing by throwing them out.


12 Merissa February 25, 2014 at 7:13 am

I hope this helps…

1. Yes, food changes when it’s canned (especially foods like potatoes or beans that absorb the liquid) so some shrinking is ok.

2. I also listen for this, not necessarily for the pop but just that the jar lid was hard to open and doesn’t come easily off. This isn’t the best indicator though, as long as the jar passes the test in the article above before it’s opened it should be fine.


13 Elaine March 31, 2014 at 8:31 pm

Just a word on the tomatoes, my Grandma & Dad both have always tod me, “No one has ever died from eating bad canned tomatoes.” If you have a bad jar of tomatoes, you will know the second you open it. The smell will tell. I am in my 30′s and still don’t can alone-I have grownups =] that I team up with. I have learned a lot and can’t wait for this years garden to provide a colorful pantry.


14 Merissa April 1, 2014 at 6:15 am

I want to caution that this isn’t necessarily true. Botulism cannot be smelled from a jar so it’s hard to detect.


15 Mathieu February 26, 2014 at 11:47 pm

Hi Merissa,
The best test you can do to verify your lids are correctly sealed is by lifting the jars by the lid (you need to remove the ring to perform the test). If there is any issue with the seal, it won’t be able to lift the weight of the jar and it will unseal.
Obviously you need to wait for the jars to cool down to execute this. This apply to reusable lids as well :)


16 Linda Jett July 19, 2014 at 11:48 pm

I canned green beans and peas and squash and tomatoes. They all sealed except 1 jar. I cooked in a water bath – the quarts 45 minutes and the pints 30 minutes. A friend now tells me that these items cannot be done in a water bath and should have been done in a PC for that length of time – not a water bath. That she would not eat them…….What do you suggest??? Thanks so much…….


17 Merissa July 20, 2014 at 9:25 am

Yes, all of those foods should be processed in a pressure canner to be safely sealed. If you just did them you should be able to re-process them in a pressure canner.


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