Ingredients

　　Two 4-pound pineapples, peeled and cut into pieces

　　2 1/2 cups fresh pink grapefruit juice

　　2 tablespoons sugar

　　3 cups chilled seltzer water or club soda

　　1 cup rum

　　In a food processor purée the pineapple in batches and strain the purée through a fine sieve into a bowl, pressing hard on the solids. Stir in the grapefruit juice and the sugar and stir the mixture until the sugar is dissolved. Chill the mixture, covered, until it is cold and stir in the seltzer water and the rum.