In a large heavy-bottomed saucepan, combine all the ingredients. Heat until the mixture begins to simmer. Decrease to medium low heat and let the mixture steep and reduce (but do not let boil) to 8 cups, about 1 hour. Refrigerate until cold.
Pour reduced liquid into a shallow pan. Freeze, stirring every 1/2 hour, until hard, about 3 to 4 hours.