Trim core, and cut pineapple into 1-inch cubes, reserving 6 large wedges. Place cut pineapple in blender and puree until smooth. (should be about 3 cups puréed) Strain mixture through a fine mesh strainer; set aside.
In a small saucepan combine the sugar and 1/2 cup water, bring the mixture to a boil, and simmer it for 5 minutes, or until it is reduced to 1/2 cup. Let the sugar syrup cool completely.
In a medium bowl, whisk together the pineapple purée, the sugar syrup, the milk, the lemon juice, and pinch of salt. Cover bowl with plastic wrap and chill in freezer until very cold about 30 minutes.
Transfer mixture to an ice cream maker and let mix until thickened, about 20 minutes. The sherbet will have a soft, creamy texture. If a firmer consistency is desired, transfer sherbet to an airtight container and place in freezer for 2 hours.