Take an 8×8 pan and line with greased foil, set aside.Place the grape juice, fruit pectin, and baking soda in a large, heavy saucepan. Heat on medium low heat until the mixture begins to boil. Reduce the heat to low.
In another heavy saucepan, combine the sugar and corn syrup. Cook over medium heat, stirring frequently until it boils and then discontinue stirring. The mixture needs to boil to the soft crack stage (280 F). You can either use a candy thermometer or test the mixture by dropping a small amount into cold water. The mixture should form fine threads that are still pliable.
When the mixture reaches soft crack temperature, carefully pour it into the warm grape juice mixture. Stir it for a few minutes and then pour into the foiled pan. If you are adding in food coloring to make the gumdrops more purple, add it in before pouring. Allow the mixture to sit overnight at room temperature to set up.
Pull the gumdrop mixture out of the pan. You can either use cookie cutters to cut out shapes or slice the gumdrops into squares. You will have to wash off residue frequently with hot water, the mixture is very sticky.
Roll the shapes or squares in sugar. Leave them out to harden for about an hour before putting in airtight containers.