I de-stemmed my mulberries by hand, which takes forever, because I wanted the fruit to stay as intact as possible, making more of a preserve texture (it also makes a dark purple mess but because the color is naturally sourced, the stains come out washing up with soap and water). It still ends up pretty mashed (cuz the stem runs down through the middle of the fruit).
4 cups smashed mulberries
1/4 cup balsamic vinegar (I picked up a lovely one last time I was in the SF Ferry Building from Stonehouse)
1 tablespoon calcium water (add calcium packet to 1/2 cup filtered water in a small jar and shake)
1 tablespoon pectin powder
2 cups rapadura sugar (this will give it a deep molasses-y flavor and won't screw up the color cuz the berries are so dark)
I clean and sterlize jars and keep lids in hot water. I follow the directions on the pectin box (and do all the stuff properly how I was taught in class and from reading the text, but here's the streamlined version):
Heat the fruit with the acid and calcium water to a boil; mix the sugar and pectin together and then add to the fruit, stirring to dissolve. Return the mixture to a boil, then remove from heat. Fill jars leaving 1/4 inch head space, add lids and rings (not too tight). Boil jars for 5 minutes on a canning rack. Remove from water bath and let sit, undisturbed overnight.
I got 5 cups of jam from this recipe.