Jam - has disaster struck? or is there still hope?

[mummyontherun]

Made plum jam this morning - its still really runny. Will it set some more, or have I got 12 jars of ruby red uselessness to look at? I have a thermometer and I let it boil for over 5 mins but the temperature never reached the majic 104 that is apparently setting point, it just got stuck at about 99. Any ideas for what to do with all these jars?

You can re-boil it. You'll have to sterilise the jars again.

Do you use the cold plate/wrinkle test?

Re-boil it, but do it in smaller batches. That way you can get the temperature higher.

Add Certo once you have taken it off the boil and it helps it set.

But don't let it boil too much or you'll get 12 jars of plum-flavoured rubber (I speak from experience).

Did you add any lemon? That's good for raising the pectin level, which is what you need for jam to set properly. Some fruit needs a helping hand in this direction (can't remember if plums do - sounds like they might though...)

I made plum jam today and it took about 10/15 minutes of boiling to reach setting point. I never use a thermometer - you can stick a plate in the freezer and dollop it on that periodically, until you can push your finger through the jam and wrinkles slightly. I'd try boiling it again.

I used about 1kg of fruit at a time (2 batches) which made 6 jars in total, and it set really quickly, so for 12 jars you may need to boil for more like 25/30 mins?

Good luck!

Plums are high in pectin usually, I only add lemon juice to things like strawberries.

Thanks for help and advice! Shame i have to re-sterilise jars as had already written and stuck pretty labels! Was torn between risk of over-boiling, and not setting, but thought thermometer would be answer....