Preserving sugar is granulated sugar with two added ingredients, natural pectin and citric acid, to bring preserves to setting point.
Pectin is a natural gelling agent. Citric acid works with the pectin and ensures that the jam will have longer shelf-life. These two ingredients give preserving sugar a slightly acid taste, and a yellow hue.
Making jam, marmalade or jelly, especially when using fruit or vegetables with a low pectin or acid content. Using preserving sugar reduces boiling time, which means the fruit retains more of its flavour.