Check it with a spoon for do the Jam Plate test. For that keep 1-2 spoons or a plate/saucer in freezer for a couple of minutes. When the jam starts getting thick and the water/juices evaporate, put some jam on the plate and keep it back in the freezer. After 3 mins. take out the plate and run your finger across the jam. It will wrinkle and not leave any mark on the plate. Jam is ready. Or, you can simply dip a chilled spoon in hot jam, it will hold onto the spoon. Jam will drip or will be runny if it is still not cooked.