Gather these berries after the first frost for best flavor. Cooking time is approximate. From the Mississippi Valley chapter of the United States Regional Cookbook, Culinary Arts Institute of Chicago, 1947. While this recipe is written in an old-fashioned way, it is perfectly safe if processed using modern methods. If you are unfamiliar with these techniques, please go to http://www.uga.edu/nchfp/how/can_home.html for the current information.
The jam is ready when the temperature registers 105C (221F) on a sugar thermometer. Simply immerse the thermometer in the jam shortly before the specified cooking time is completed, keeping it away from the base and the sides of the pan. Leave in position until the temperature has been reached. Boil a little longer if necessary.
Drop a spoonful of the jam on to a chilled saucer and leave to cool slightly. Push your finger through the jam: if the surface wrinkles, the jam is ready. Return to the heat and boil a little longer if necessary.
Using a large wooden spoon, lift a little of the jam out of the pan. Let it cool slightly then tip the spoon so that the jam drops back into the pan. If it has been boiled for long enough, drops of the syrup will run together along the edge of the spoon and form flakes which will break off sharply. Boil a little longer if necessary.