This week I opened a forgotten jar of 1999 Plum Jam. It was slightly discolored but tasted good.
When I made jam or jelly, I boiled it and put it in jars. The flat lids were kept in just less than boiling water and put on the clean tops fast, then the rings screwed down tightly. Later I would punch each top to see if it would pop down, if not it went into hot water for a boil. Then I'd let them set for a couple of days.
If it was thick, it was labeled jam or marmalade or jelly. If not, then it was labeled Pancake Syrup!!!