A simpler method might be make a sugar syrup solution with 2 cups sugar to 1 cup hot water. mix in a blender let cool. Make four or five measured samples of wine say 1/4 cup=60ml per sample. use the first as a control. add 1/4 tsp-1.25ml to first, 2 X1/4 to second, 3x1/4 to third and so on. Taste, the final measurement tool, to find the level you desire. Sometimes prudent to go one sample more than one that you chose to make sure level of sweetness is what is desired. Calculate using ratio math amount of sugar syrup to add to larger batch. don't forget to add sorbate and k-meta once blend is made. wait one week or so to insure fermentation does not restart. bottle.