In a bowl, combine measured jam or jelly and 2 Tablespoons sugar for each cup of jam or jelly. Place in small saucepan and place over low heat, stirring until the powdered pectin is dissolved. Pour into clean containers. Cover with tight lids. Let stand in refrigerator until set, then store in refrigerator or freezer.
Fermentation is caused by yeasts growing and multiplying in a warm, moist, food-rich environment.
Live yeasts and molds live on the surface of unheated fruits. When sugar is added and the fruit sits at a very warm room temperature, all the requirements for yeast growth are fulfilled. Store the uncooked jam in the refrigerator so the yeasts are not at an optimal growing temperature. Soft or fuzzy white spots indicate mold growth. If this is the case, throw the jam out.