Mix the grapefruit juice and water in a medium bowl and add the corn syrup.
Pour into an ice cream canister and pour into an ice cream maker.
How to freeze:
Pour the prepared mixture into a 5x9 loaf pan. Place in the freezer. Cover with cloth or plastic. Keep it in the freezer and freeze it. Scrape the jamahua contents with a fork. Serve immediately or freeze prepared ingredients further. Break it into small pieces. Spoon into a chilled food processor. Grind with a metal grinder until very smooth. Serve immediately or place in the freezer to firm up the whipped topping.