I can’t tell you the number of times I have been asked a question along the lines of “Can I reduce the sugar in this recipe?” or “Could I substitute honey for sugar?” The short answer is most likely ‘yes’ in both instances, but you have to understand why sugar is part of the recipe in the first place and what will happen if you decide to alter the amount.
Jams, jellies and marmalades (in general) are all made from a balance of four ingredients. The proportion of each in relation to the other is required to achieve the right ‘set’.
- Fruit, sugar, pectin and acid
Sugar plays an important role in two ways; set and preservation
Too little sugar, acid or pectin in relation to the fruit and you jam will remain liquidy.
Too much sugar, acid or pectin and your jam will be stiff.
When you cook jam it is cooked to 220 degrees F and at this temperature, the heated sugar will bond with the pectin and provide your jam with the desired structure or ‘set’.
Products higher in sugar have a much longer shelf life than those will lower sugar. This means that if you cut the sugar in your recipe in half, two things will happen. You will end up with a runny jam and its shelf life will be drastically reduced.
If a runny jam that is more like syrup in consistency that only lasts in your pantry for a limited period of time is ok with you, then yes feel free to reduce the sugar.
Note: If you want to make a jam with less sugar, use a pectin designed specifically for this purpose and follow the enclosed directions closely.