canning question: lids unsealing at random times

[bethanyhoffman]

I do a lot of canning-started a few years ago but got a bit of a bug; I would classify myself somewhere between expert and novice, at least within my chosen domain of sweet jams/jellies/preserves. Today I was quietly reading and heard the telltale canning ping from an adjacent room-- sure enough a jar of quince marmalade I had processed about two days ago lost its seal-- the center of the lid had popped up. I decided to take the opportunity to check through my whole stash [about 500 jars- yes I've gone a little crazy] and found three other jars whose lids had popped up. I had a similar experience a few months ago. I always check the seal on my lids at least twice before storage- once after they come out of the water bath and once as i check/label/store them, usually 24-48 hours later. I would categorize myself as high but not super-high on the scale of canning 'hygiene' -- I always use new lids, heated in boiling water before applied, keep the jars in a low oven before filling, etc.. I have a rough idea of appropriate head-space, but i don't get out the ruler for each jar.

I have two questions-- anyone know why this happens/how to prevent it, and also if you really need to throw such jars away? I always throw them away though it seems wasteful. In spite of dire warning that tell us to treat unsealed jars like nuclear waste, I have never seen any bulging lids, bubbling or leaking contents, discoloration, mold or other obvious signs of rancidity. In fact, when I open the jar to throw its contents away, the lid is usually pretty tightly attached and has to be pried off even though the center popped up. The contents have never looked any different than their sealed compatriots as i guiltily glop them into the disposal.

From my various perusals, the late-stage lid failure is likely due to a 'poor original seal,' but i am pretty careful about my canning procedure, processing times, etc.. I don't, unfortunately, have a root cellar or similarly dark, stable environment for storing my jars, but i do put them in a closet or room with the blinds drawn in the downstairs of my house where the temperature fluctuates least. I guess the only thing possible culprit I have noticed is with pretty much every case of new jars i get the lids are stuck tight to the jars, have formed some kind of seal, and have a strong jar rim indentation. Is there any chance these new lids have effectively become 'used' via the thermal changes the empty jars have undergone through their brief lifetime, and are not creating a good seal? Any help would be appreciated-- thanks in advance (and sorry for the long rant!)

[John DePaula]

Is it possible that you're using water that's too hot to prep the lids? I thought the water should be hot but not boiling (~180F).

Otherwise, I'd say your 99.2% success rate is pretty good!

[annecros]

A couple of years ago I was having a sporadic problem, and traced it back to one box of bad lids - because it was from only two batches that I had done back to back.

I let the manufacturer know about my problem, and they sent me a case of jars and lids.

[bethanyhoffman]

Thanks for both of these ideas. Maybe boiling water is too hot for prepping the lids (though they go right into a boiling water bath...); I'll try reducing my water to green tea temperature for future batches.

Anne, I don't think it is a single batch of lids in my case because the failures were all from different batches of jam over a four month period, but your comments make me wonder if there isn't just some percentage of 'duds' mixed in among the jars that lead to a small failure rate. I guess you're right, John, that it's a small failure rate overall. I'd say in the course of the average year, I still have ~ 10 jars fail in the way I described, but even so a 2% failure rate isn't wretched.

On at least a few occasions I've witnessed jar centers popping back down (especially if I catch them immediately and move them to a cool environment like the refrigerator). As a result I've developed a mild paranoia that other seals are weak such that the lids cycle in and out of a 'sealed' state in storage, maybe as the temperature fluctuates in the storage environment, and I might be none the wiser as I select an apparently sealed jar to eat. But then, there is no food storage system that frees us from all contamination/spoilage issues, and I've never had a problem, so I suppose I should really redirect my paranoia to a more fruitful topic. Anyway, thanks again for these suggestions.

[sparrowgrass]

These are jams and jellies with lots of sugar, right? This is not the USDA answer that I have to give at work, but our grannies mostly didn't water bath their jams and jellies. My grandma sealed hers with parafin and a screw on lid, and never killed anybody. (That I know of. )

You might get some mold on an unsealed jar, but the sugar and acid take care of the bacteria and botulism. Toss the moldy ones--they will taste bad.

Another reason for bad seals is imperfect jars. Be sure to run your finger around the rim to check for chips or bumps.

You are doing well to have so few bad seals!!

[bethanyhoffman]

thank you very much for this 'unofficial sanction,' sparrowgrass! I am indeed talking about high sugar products [with a fair bit of extra lemon juice or citric acid too because i like a tart edge to my jams]. Some jams I don't mind so much throwing away, but then there are the coveted/expensive/super-labor intensive sorts, like sour cherry preserves (come to think of it, those are labor-intensive, expensive, AND my most coveted variety).

Also, I must admit that I don't really check the jar rims with my finger (just eyeball them for cracks or chips). I will start doing so. So, any jars with small bump or imperfection on the rim will prevent a good seal?

These are jams and jellies with lots of sugar, right?  This is not the USDA answer that I have to give at work, but our grannies mostly didn't water bath their jams and jellies.  My grandma sealed hers with parafin and a screw on lid, and never killed anybody.  (That I know of.  )

You might get some mold on an unsealed jar, but the sugar and acid take care of the bacteria and botulism.  Toss the moldy ones--they will taste bad.

Another reason for bad seals is imperfect jars.  Be sure to run your finger around the rim to check for chips or bumps.

You are doing well to have so few bad seals!!

←

[sparrowgrass]

A chip or bump could prevent a good seal. I just run my finger over the glass as I wash them out after use, and discard any that are not perfect, and check them again before I reuse them.

I also inspect the flats (lids) before I put them into the hot water--I have found a (very) few that had gaps in the rubber.

Other things that might cause a problem is an air bubble in the jam, filling the jars too full, or a bit of jam on the rim.

Again, I would like to say that USDA/Extension would tell you to toss any jars that you find in the pantry with a bad seal. And, I guess it is always better to be safe than DEAD.

Edited December 11, 2008 by sparrowgrass (log)