What Causes 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 on top of jelly that has been opened and allowed to stand are due to evaporation of liquid. Tartrate crystals in grape jelly may occur if juice has not been allowed to stand overnight and then strained through a double thickness of cheesecloth before preparing jelly.