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Canning -- Jams and Jellies

Why do crystals form in jelly?

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The high concentration of sugar in a jelly product makes it susceptible to crystallization. There are several reasons for crystal formation. 1) The jelly mixture may contain too much sugar, thus the sugar comes out of solution as crystals. This may be because too much sugar has been used or because the jelly was cooked too long, thus evaporating too much water (making the sugar concentration higher). 2) The crystals may form if the jelly mixture is not cooked long enough. When sucrose is heated in the presence of acid, it breaks down into glucose and fructose. This is referred to as invert sugar. Invert sugar has less tendency to crystallize than sucrose. 3) Crystals may form at the top of an opened jar of jelly as liquid evaporates thus giving a high sugar concentration in that area.

PREPARED BY: Angela M. Fraser, Ph.D., Associate Professor/Food Safety Specialist, and Carolyn J. Lackey, Ph.D., R.D., L.D.N., Professor/Food and Nutrition Specialist, North Carolina State University (August 2004)

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