Place the water and diced butter in a saucepan over medium heat, cook gently until the butter has melted, then bring to a rolling boil. Remove the pan from the heat and pour all of the flour in at once. Stir with a wooden spoon until the mixture is smooth and comes away from the sides of the pan. Let cool slightly.

Place the warm flour mixture in the bowl of a mixer. Add the diced Brie and mix with the paddle attachment until well combined. Mix together the egg and the salt and gradually add to the dough, beating well between each addition. Stir in the grapes.

Deep fry 5 to 6 spoonfuls of batter in 350 F oil, turning the fritters occasionally as they cook. Cook for 3 minutes, or until the fritters are completely puffed and a dark golden brown. Drain well and continue with remaining fritter batter. Serve warm.