There are several fruits that have the classification of medium pectin and peaches as well as rhubarb and strawberries fall into that category. Because peaches have a moderate amount of pectin in them already, this makes them ideal for jam recipes without pectin. This is why we add lemon juice as well. The lemon juice contains pectin and helps in attaining the jam consistency in this recipe. For other types of fruit, cornstarch can be added instead of pectin to help thicken the jam.