Why Does Jam Crystallize and Turn Sugary Over Time?

Sugar crystals in jam can be associated with incomplete dissolution, recipe proportions, or excessive cooking. Distinguish crystals from signs of spoilage.

Prevention. Follow the fruit, sugar, acid, and pectin quantities in a tested recipe. For reduced sugar, use an appropriate pectin and recipe; adding ordinary pectin does not permit reducing sugar in every recipe. Do not improvise a one-for-one substitution with honey or molasses.

Jars and processing. Prepare jars as directed and follow hot-filling and sealing steps. For shelf storage, apply the appropriate boiling-water process for the jar size and altitude. Hot filling and closing alone should not be considered sufficient.

Crystallized jam. In jam known to have been prepared and stored safely, crystallization alone may be a quality issue. If there is mold, unexpected gas production, or spoilage, discard all of it; do not scrape the surface or try to rescue it by heating. Follow the recipe's storage instructions after opening and for refrigerator or freezer jams.