Jam making

[shivvy]

The sugar content in store-bought jams and in jam recipes is very high.
Is there any negative impact on the jam if I were to reduce the amount of sugar in a recipe?
I know it will be less sweet but does it have any other impact eg does it effect how the jam sets etc?
Thanks

[heathfield]

Sugar acts as a preservative as well as a sweetener. If the sugar content is less that 68% there's a risk of the jam going mouldy. If the percentage is a good bit higher, the jam could crystallise.
Jam labels showing less than 68% sugar will probably have glucose syrup added, which is doing the same to the jam as sugar would. The friut will also contain sugars and these won't be listed in the ingredients, but will help raise the total percentage present.

[shivvy]

Thanks heathfield - great answer.
So would it be ok if I made jam with half the sugar, but made a smaller quantity of so that it gets used up more quickly therefore avoiding the liklihood of it going mouldy?
Is the taste very much different with less sugar?

[Mirror]

heathfield is 100% correct. i've tried using less sugar and indeed after a week mold was forming on the surface.

[heathfield]

If you use only half the sugar, the jam may not set. Pectin, which helps jam set, is naturally present in some fruits, but with others you may be advised in a recipe to add some. The problem is that the pectin needs a fairly high sugar content before it will work properly. But If Mirror's had success with less sugar, then making a small amount could be worth trying.