An instant read candy thermometer is the easiest way to know when jam is ready! The gelling point of jams and jellies is 220°F. If an instant read thermometer isn't available, place a small plate in the freezer for 10-15 minutes, remove and spoon a dollop of hot jam onto the cold plate. Once the jam is cool to the touch, run your finger through the center of the dollop, the jam should clearly separate into two and not puddle back into a single dollop.