Preheat oven to 400 degrees F (200 degrees C). Grease a muffin tin with butter.
Stir all-purpose flour, whole-wheat flour, sugar, baking powder, cumin, baking soda, garlic powder, and salt in a large bowl. Blend butter into flour mixture with two knives or your fingers until mixture resembles coarse cornmeal.
Beat milk, reserved garbanzo bean liquid, lemon zest, and egg together until smooth. Stir into dry ingredients until just moistened. Fold garbanzo beans and grapes into batter until incorporated. Spoon batter into prepared muffin tin.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 15 minutes.