I don't use sugar in my jams. There is a pectin for low/no sugar and I use that. One year I boiled down white grape juice for sweetener. This year I made a batch of strawberry jam with less than a teaspoon of honey (to retain color). It was not necessary for flavor or set. Best strawberry jam ever. My friend grates an apple into her jams says it helps. I have not tasted it though to see if it's sweeter, better than the one I did.