Combine the berries and mint in a large bowl.
Combine the Champagne, sugar, salt, and vanilla bean in a medium saucepan over medium-high heat. Simmer until the sugar dissolves and the mixture is syrupy, about 15 minutes. Remove from the heat and allow to cool until just warm. Remove the vanilla bean. Add the lemon juice and zest and stir to combine. Pour the syrup over the berries and toss to combine. Cover and refrigerate for at least 1 hour before serving.
Makes about 4 quarts, 16 servings