Preheat oven to 350. Peel, seed, and finely chop apples. Grease dozen muffin cups or line with paper liners; set aside. Combine dry ingredients in medium bowl. Combine and add eggs, apple juice concentrate, melted butter, and vanilla; mix just until dry ingredients are moistened. Stir in apple and walnuts. Spoon batter into prepared cups, filling each cup 0.75 full. Bake 25 minutes, until golden brown. Let stand in pan on wire rack 5 minutes. Remove from pan. Serve warm or at room temperature. Cooled muffins may be wrapped securely and frozen up to 3 months.