Preheat the oven to 350°. Butter and flour a 9-inch springform pan. In a small bowl, whisk the flour with the salt and baking powder. In a large bowl, whisk the eggs with the granulated sugar until pale yellow. Whisk in the milk, olive oil, melted butter, lemon zest, orange zest and vanilla. Fold in the flour mixture, followed by 1 1/2 cups of the grapes. Scrape the batter into the prepared pan.