When Canning Jars Won’t Seal

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Canning Easy-Peasy Grape Juice.


Anyone who cans food has had the experience – you make your jam or jelly, or process fruits and vegetables, and one or more jars don’t seal. Frustrating but not unexpected. Canning is an organic, biological practice. It cannot be cut and dried and you have to expect variations. Here are some of the common problems and reasons why jars won’t seal.
Getting a perfect seal depends on several factors. These include the quality and thickness of the sealing compound, damage to jars, lids or rings, cleanliness, the temperature of the food and whether you tighten the rings properly. Whether you water-bath or not, in the case of jams and jellies, has nothing to do with getting a good seal.

Making applesauce with a food mill.


I’m as frugal as the next girl, but I also recognize that when I’m working with non-standard canning jars, the chance of something not sealing is a little higher. That’s because those jars don’t necessarily have a perfect fit with a standard canning lid and ring. Don’t let that stop you, just be prepared for a failure or two. Jar rims must be perfect – the slightest chip means a seal may not occur. The same applies to a lid or ring that is even slightly bent. You can still use these jars and lids for storage or make fermented veggies in them (fermented foods don’t have to be canned – a huge time-saver during a busy processing time). And as an aside, you can reuse commercial jars with lug tops for jams and jellies. Again, that means a slightly increased risk of jars not sealing – about one in 20, in my experience.

No water bath required.


User errors are the next most likely problem. If you don’t tighten the rings properly, you won’t get a good seal – tighten to the point of resistance. A drip of jam or piece of whatever you’re canning that lands on the jar rim will interfere with a seal – always wipe clean or, as I do for jams and jellies, use a pitcher to pour in the liquid. Leave the right amount of head-space if you are water-bathing or pressure canning so food doesn’t bubble up. This also helps prevent exploding jars. Air bubbles can also affect the seal – they’re more likely with dense foods like squash or pumpkin. Use a clean knife to pop bubbles and let them escape before putting on the ring.

Please note the date! This picture was taken in 2015. Thirty-plus years and still sealed.


The heating and cooling processes are also important to a good seal. While you don’t have to water-bath jams and jellies, you do need to make sure the liquid is at a full boil when you pour it in the jar. Work quickly, so the jar and filling remain as hot as possible. If you’re processing, make sure the temperature is correct and that you leave it in for the right amount of time. Once your jars are out and cooling, leave them alone until completely cool – this usually takes 24 hours. Always check seals before storing. If the center button isn’t depressed, store in the refrigerator and eat soon. Jams and jellies will store for a few weeks, but veggies and meats should be eaten within a week or so. You can also freeze jars with failed seals, but in most cases, filling to the proper level doesn’t leave enough room for expansion during freezing, so I don’t recommend it unless you have an inexhaustible source of jars and don’t mind cleaning up a mess in the freezer.

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3 Responses to When Canning Jars Won’t Seal

  1. littleleftie says:

    Actually, your reply echoes my own experience. To me, not worth the time or effort. Some friends of mine can their own moose meat. But that is different, as they only use it in stews or shepherd’s pie. Texture isn’t as much of an issue, they say, because of how they use it. But I appreciate your candor. Thanks alot!

  2. littleleftie says:

    What kinds of meats do you can? Can you do a post about that?

    • Bee says:

      I haven’t canned meat in forever, and wouldn’t start again unless the power went out permanently and it was the only way I could preserve it. By the time it’s cooked enough to be safe, it’s pretty much cooked to death and I don’t think it has any flavor (think canned chicken). The texture really suffers, too. I think Ell cans tuna occasionally, but otherwise we both prefer to freeze meat. Frozen meat, like steaks, chops and roasts can be cooked without thawing, which means it’s juicy and tender. If any of you other readers can speak to this issue, please step up!

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