Breaking Jam Jar

I’ve just had a very bizarre jam-making experience and I’d like to know what you other jam-making people make of it, if you wouldn’t mind.

At about this time of year, I make redcurrant jelly (lovely with lamb or duck) as we are very fond of it. I’ve been making it for donkeys years, along with other jams as and when.

Today, having cooked and strained the fruit overnight, I heated the resulting juice in a big pan, added the sugar as usual and heated gently, stirring, until the sugar dissolved. Then I increased the heat so that the liquid came to a rollicking boil, tested it after a few minute to see if it was at setting point. It was, so I turned the pan off.

The jars were hot, having been warming in the oven as usual. I took one out, put it on a mat and started to ladle the jam into the jar. At this point the jar cracked spectacularly in big zig-zags starting from the bottom and working up (interesting sound effects).

This has never happened before as I’m assiduous in heating the jars. Any ideas? I used Le Parfait jars as I always do and they seemed in good condition.

Have the jars been used before? Maybe they’ve just reached their “jam-by” date? If you hadn’t heated them of course the hot jam could have caused rapid thermal expansion but that doesn’t sound like it was the reason if you pre-heated them.

Or perhaps there was a small chip or stress fracture in that jar?

Otherwise I would suspect a breach in the space-time continuum.


I wondered about that but I thought I’d checked carefully first - perhaps my eyesight is worse than I thought :roll_eyes:

Your eyesight is obviously better than mine, because when I read -

I saw " I’ve been making it from donkeys ears"

SpecSavers etc . . . . . . .


Hmmm… reminds me of the discussions I have with my partner in the mornings when he says something and I hear something quite different, then I reply and he hears something quite different :roll_eyes: Age, eh?

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What was the mat made of, how thick was it, and was it especially cold?

It happens.

Glass can be temperamental if it’s been dropped - taken a hit or a sharp knock. You can’t always see it.

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cork, thick, not at all!

The right answers! In that case, I’d go along with chrisell and suggest that the glass contained some hidden defect - possibly a manufacturing problem (e.g. a tiny air bubble) or as a result of having been dropped. The addition of the hot liquid caused stress fractures to emanate from the weakest point. Just one of those things, basically :slightly_smiling_face:


This may or may not be related to your experience, but a while ago one of my Duralex glasses literally exploded in the washing up. Apparently they are made to crumble into little pieces rather than shatter into large shards, and will occasionally spontaneously self-destruct. A pity, it was the only one that was just the right size for a couple of shots of whisky.

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Any toughened glass can do that and they will all break into tiny fragments because of the way the toughening process sets up stresses in the material.

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A good time to mention Prince Rupert’s Drops.


Crossed post :grin:

That happens to us a very lot. Glitches in the space/time continuum…

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And Oscar and Lucinda.