Fruits should be at their peak of freshness for best flavor and color. Canned or frozen unsweetened fruit or juice can be used.
Pectin is necessary for jelling. It is naturally present in some fruits or can be added in a powdered or liquid form. Do not substitute one form of pectin for another; add pectin exactly as specified in the recipe. Using less pectin than the recipe suggests is likely to produce a syrup rather than a jelly or jam. Be sure to use the pectin by the date indicated on its package.
Sugar acts as a preservative, develops the flavor, and aids in jelling. Always use the amount of sugar specified in a recipe.
Acid is needed for proper jelling and for flavor. When fruits are low in acid, recipes call for adding lemon juice or citric acid.
Prepare only one batch at a time. Do not try to double the recipe.
Vigorous boiling is part of jellymaking. A full rolling boil is one so rapid that you can't stir it down. To prevent it from boiling over, fill a pan no more than one-third full.
A mixture will sheet off a spoon when it has reached its jelling point. To test it, dip a metal spoon into the boiling mixture, then hold it over the kettle. If mixture is done, two drops will hang off the edge of the spoon, then run together in a sheetlike action. You can also use a candy thermometer to find when the jelling point is reached (8 degrees F above the boiling point of water -- or 220 degrees F at sea level).
Foam is a natural result of boiling. Quickly skim it off with a large metal spoon before ladling jelly into sterilized jars. Process jellies and jams in a boiling-water canner. For locations with altitudes below 1,000 feet above sea level, process for five minutes. Add one minute for each additional 1,000 feet.
After processing, let jellies and jams sit for 12 to 24 hours or until set. Use within six months.