Place a rack in the middle of the oven, and preheat to 375 degrees F.
Whisk together flour, baking powder, baking soda, and salt.
Beat butter with 2/3 cup sugar using an electric mixer on medium speed, until light and fluffy. Add eggs one at a time, beating well after each addition. Beat in zest.
Add flour mixture in two batches, alternately wtih wine, beginning and ending flour, mixing until just incorporated.
Toss grapes with remaining tablespoon flour, then fold into batter.
Divide batter among muffin cups. Sprinkle with remaining 2 tablespoons sugar. Bake until golden and springy to the touch, 18-20 minutes. Cool in pan 5 minutes, then loosen with a knife, and remove. Cool to warm, 5-10 minutes more. Dust with confectioners' sugar before serving.