Would you be willing to share your recipe for sugar free jam?
The sugar free recipe was modified from the Ball jar of Low or No-Sugar Needed Pectin. There is a table on the inside of the label for canning various fruit. For each 2 cups of crushed strawberries, use:
2 cups crushed strawberries
1/3 cup unsweetened fruit juice (I use apple)
3 tsp lemon juice
1 1/2 tbs pectin
You can use up to 10 cups of fruit, which is what I used. Combine all of the above ingredients and bring to a boil. Here's where I differ from the instructions. The label says to add your chosen sugar substitute and bring to a rapid boil for 1 minute. I've found that most of the sugar substitutes get very bitter when boiled, so I remove from the heat after boiling for 1 minute with the pectin. I use a combination of concentrated stevia (NOT the one that measures like sugar) & agave syrup, and go mostly by taste. For the 10-cup batch of strawberries, I used 2 tablespoons of stevia and added the agave until it tasted right, almost 2 bottles of 23.5 oz by weight. The BWB for 10 minutes, rest in the water for 5 minutes, remove & cool. There is some fruit float, so once he jars are cool, I start rotating them to distribute the fruit. I got 12 half pint jars.
I use the same method for making sugar-free blueberry jam. Before using the combination of stevia/agave, I had tried all sorts of sugar substitute combinations - splenda, nutrasweet, straight stevia, straight agave. They all turned out so bitter, except the straight agave. DH read about them turning bitter under heat, so we came up with adding the substitute after the heat was turned off. This works great for us.