Has anyone used a jam thermometer?

[psafloyd]

After my twelve jars of greengage jam did not set and throwing a big tantrum I today bought a jam thermometer. Setting point of jam as indicated on said gadget, 105 degrees. Reboiled the jam like a thing possessed and it would not go above 100 degrees. Any ideas?

If you watch the jam boil, you will see the bubles change, giving it a certain glassiness. It will generally pass the cold plate test, then.

You could always try making it in the microwave. My outlaws do it this way and it produces passable results. I only don't like that they filter out all the bits.

Finally, perhaps you didn't have enough pectin in the greengages. And in any case, does it realy matter? if not set like a jam, is there anything wrong with a 'preserve' that is a little runy, if it tastes good? That's what i call mine if they don't set 'properly'.