Pour the sweet juice in a 38 x 25-cm (15 x 10-inch) Pyrex dish. Freeze for 1 hour. Stir with a fork, scraping the sides of the dish. Return to the freezer, stirring every 30 minutes until the mixture is crumbly, about 2 hours 30 minutes to 3 hours (you should stir a total of 4 to 5 times).