What is the reason of forming sugar crystals in different kinds of jam?
The low rate of acidity of the product , in other words , more than the standard rate as well as using much sugar in formulation and improper baking cause the acceleration of forming sugar crystals especially during keeping the product in low temperatures such as in the refrigerator. To solve such a problem , you may pour the jam with sugar crystals in a container and add a little citric acid or lemon juice before heating it again.