I usually freeze my jam into large blocks using tupperware and then transfer them into vacuum sealing bags. After sucking the air out, I let them defrost and th

I usually freeze my jam into large blocks using tupperware and then transfer them into vacuum sealing bags. After sucking the air out, I let them defrost and then they stack nicely as flat packs of jam, ready to be cut open. No glass to break, no worry about not getting all of the air out, and easy to inspect from all sides to see if anything has started growing in there. Also works well for other "liquidy" things people usually put into jars.