Few fruits contain enough of the natural jelling agent, pectin, to make thick jams without long periods of cooking. This lack can easily be avoided by adding either natural pectin-rich fruit juices such as apple, currant, or lemon, or by adding commercial pectin such as “Certo, ” available in grocery stores. By following these basic steps, you can make a wide variety of jams, but it is always best to check the directions on the brand of pectin you are using and to stick with one that gives you consistently good results. Remember that a runny jam makes excellent dessert topping, so there are, in effect, no failed jams.