Start by thoroughly washing the grapefruit peel to remove any wax or residue. Then dice the whole fruit, peel included, into 2-inch pieces. The peel adds depth of flavor and aroma, enhancing the syrup's complexity.

In a medium saucepan over medium heat, combine the sugar, water, and diced grapefruit. Stir gently until the sugar fully dissolves into the mixture.

Allow the mixture to simmer gently for about 15 minutes. This step helps the grapefruit flavor infuse into the syrup while thickening it slightly.

Once finished, remove the saucepan from the heat and allow the syrup to cool to room temperature.

Strain the mixture through a fine mesh strainer to remove the fruit solids and zest. Press the fruit gently with the back of a spoon to extract as much flavor as possible.

Transfer the finished syrup to a clean, airtight container and refrigerate. The syrup will stay fresh for up to three weeks.