Sugar

Sugar is not only sweet. In this encyclopedia it has at least three jobs, and mixing them up is how people invent unsafe jam.

Gel and preservation in jam. Ohio State: sugar must be in proportion with pectin and acid to make a gel; it also limits microorganisms and contributes taste ¹. You cannot swap sucralose into a regular-pectin canned jam and keep the same process; NCHFP is explicit that Splenda does not provide sugar’s preservative properties, and regular pectin formulas require their sugar ². The NCHFP strawberry jam uses 8 cups sugar with 5½ cups crushed fruit ³. Change that and you have left the tested process. See Jam and Pectin.

Fermentable in wine. Grape berries already hold glucose and fructose. Yeast turns much of that sugar into alcohol. Residual sugar is sweetness in the glass. Added sucrose in a kettle and native sugar in a grape are the same class of molecules in different foods. Wine is the craft.

Baking. A little sugar in dough is food for yeast and color in the crust. It is not jam’s 1:1 fruit contract.

If you want shelf-stable canned jam, sugar is a formula ingredient, not a preference. Food safety before you reduce it.