01 - Zest one grapefruit using a fine grater, being careful to avoid the bitter white pith. Set the zest aside for later use.
02 - Juice all grapefruits to obtain approximately 1.5 cups of fresh juice. Strain through a fine-mesh sieve to remove pulp and seeds.
03 - Combine sugar and water in a small saucepan. Place over medium heat and bring to a gentle simmer, stirring constantly until sugar completely dissolves. Remove from heat and allow to cool to room temperature.
04 - In a large mixing bowl, whisk together the strained grapefruit juice, reserved zest, lemon juice, salt, and cooled simple syrup until fully incorporated.
05 - Transfer the mixture to the refrigerator and chill for at least 1 hour to ensure proper freezing and texture development.
06 - Pour the chilled base into an ice cream maker and churn according to manufacturer's instructions, typically 20–25 minutes, until the mixture reaches a thick, slushy consistency.
07 - Transfer the churned sorbet to an airtight, freezer-safe container. Cover tightly and freeze for at least 4 hours or until firm enough to scoop.
08 - Remove from freezer and let stand at room temperature for 5–10 minutes before scooping to soften slightly for optimal texture.