Preheat the oven to 350 F. Line 12 muffin tins with foil cup liners and set aside.
In a small bowl, mix the graham cracker crumbs with the butter. Place 1 tablespoon of the graham cracker mixture into each muffin cup and gently press to form a crust in the baking cups. Bake for 7 minutes; set aside.

Combine 1/4 cup of the grape juice concentrate, lemon juice, and grapes in a small sauce pan over medium heat. Meanwhile combine the remaining grape juice with corn starch and mix well, then add to the sauce pan. Bring the mixture to a boil for 1-2 minutes until thick. Allow to cool. Once this mixture cools, pour into a blender and blend until smooth. Add the softened yogurt and blend for a few pulses until just combined.

Place about 4 tablespoons of the grape-yogurt mixture into each muffin tin. Place in the freezer for 4 hours or more. Serve with small clusters of frozen grapes and enjoy.