Why do crystals form in jelly?
Crystals throughout the jelly may be caused by too much sugar in the jelly mixture or cooking the mixture too little, too slowly, or too long. Crystals that form at the top of jelly that has been opened and allowed to stand are caused by evaporation of the liquid. Undissolved sugar sticking to the sides of the pan may also be a source of crystals in jelly. A few crystals usually remain in freezer jam. Some pectin manufacturers include corn syrup in recipes for freezer jam to help prevent this. Crystals in grape jelly may be tartrate crystals. To prevent them, refrigerate juice for 24-48 hours. Then strain juice through two thicknesses of damp cheesecloth to remove crystals.
Barbara Willenberg, Nutritional
Sciences, University of Missouri-Columbia
Last update: Tuesday, May 05, 2009