There are a couple of ways to ensure the jam is ready: Thermometer: Use the thermometer to check the temperature of the jam. It needs to be 105 C or 220 F, the point where sugar reacts with the pectin and forms a gel. Dripping Method: When the jam starts to leave the sides of the pan and you see it thickened, scoop up the jam in the spoon and drip it down in the pan. If the dripping is easy and quick, it is not ready. However, it the jam takes a while and then drips, it is ready. Freezing Method: Put a plate in the freezer for 10 minutes. Once you think the jam has thickened and set, take out the plate of the freezer, put half tea spoon of jam on the plate and run your finger through the jam on the plate. If there are wrinkles and the texture feels like a gel, the jam is ready. If not, you should cook the jam for some more time. Check out this video on testing jam.