01 - In a small saucepan, combine the 3/4 cup granulated sugar and 1/2 cup water. Heat over medium heat, stirring continuously until the sugar is completely dissolved. Remove from heat and allow the simple syrup to cool to room temperature.
02 - Juice the 4 large pink grapefruits. Strain the freshly squeezed juice through a fine mesh strainer to remove any pulp and seeds. Measure out 2 cups of the strained grapefruit juice.
03 - In a spacious mixing bowl, combine the cooled simple syrup, the 2 cups strained grapefruit juice, 1 tablespoon fresh lemon juice, the zest of 1 pink grapefruit (if using), and 1 pinch salt. Stir thoroughly to ensure all ingredients are well incorporated.
04 - Cover the mixing bowl and refrigerate the sorbet mixture for a minimum of 1 hour, or until it is thoroughly chilled.
05 - Pour the chilled mixture into an ice cream maker. Churn according to the manufacturer's specific instructions, typically for 20-25 minutes, until the mixture achieves a soft, sorbet-like consistency.
06 - Transfer the freshly churned sorbet into a freezer-safe container. Cover the container tightly and place it in the freezer for at least 3 hours, or until the sorbet becomes firm.
07 - Before serving, remove the sorbet from the freezer and allow it to sit at room temperature for approximately 5 minutes. This will soften it slightly, making it easier to scoop and serve.