Test a lid by pressing gently. If it flexes, the seal is not present. Boil for up to an hour. Otherwise, you will have to begin again. Pectin and acid, natural substances found in fruit, promote jelling and shelf life.
Sugar is the third component in the equation.
Well balanced preserve recipes call for appropriate amounts of acid, pectin and sugar. Our recipes do not call for the use of commercial pectin. Jams made the traditional way, are easy to prepare and they bring forth the flavor of the fruit with the most basic of ingredients. Knowing when your jam is ready is something that comes with experience, but there are two tests you may use. First, place a ceramic saucer in the freezer just before you begin your jam making.