01 - Zest one grapefruit using a fine grater, taking care to avoid the bitter white pith. Set zest aside for later use.
02 - Juice all grapefruits to obtain approximately 1.5 cups of juice. Strain through a fine-mesh sieve to remove pulp and seeds.
03 - Combine sugar and water in a small saucepan. Bring to a simmer over medium heat, stirring continuously until sugar completely dissolves. Remove from heat and cool to room temperature.
04 - In a large bowl, whisk together grapefruit juice, reserved zest, lemon juice, salt, and cooled simple syrup until fully incorporated.
05 - Refrigerate mixture for at least 1 hour until thoroughly cold, ensuring proper texture during churning.
06 - Pour chilled base into ice cream maker and churn according to manufacturer instructions, approximately 20–25 minutes, until mixture reaches thick, slushy consistency.
07 - Transfer churned sorbet to freezer-safe container. Cover tightly and freeze for minimum 4 hours until firm.
08 - Allow sorbet to sit at room temperature for 5–10 minutes before scooping to achieve optimal texture.