Follow storage directions carefully for low-sugar jams and jellies. If your recipe can't be processed in a boiling-water canner or frozen successfully, you can only leave the product in the refrigerator about three or four weeks. Discard all moldy jams and jellies. Fruits can be frozen or canned for making jams or jellies at a more convenient time. Preserve the fruits unsweetened.
Frozen fruits tend to collapse when thawed, which makes accurate measurements difficult.
You also can use unsweetened, commercially canned or frozen fruit or fruit juice. Thickeners with low-sugar jams and jellies Jellies and jams that contain modified pectin, gelatin, or gum may be made with noncaloric sweeteners. Jams with less sugar than usual also can be made with concentrated fruit pulp, which contains less liquid and less sugar. Two types of modified pectin are available for home use. One gels with one-third less sugar.