Add the cubed pineapple to a blender and blend until completely smooth. Strain through a fine-mesh sieve, pressing gently to extract the juice. Discard the pulp and set the pineapple juice aside.
In a small saucepan, combine the sugar and 1 cup water. Bring to a gentle simmer over medium heat, stirring until the sugar fully dissolves. Remove from heat and stir in the freshly grated ginger. Let steep for 5 minutes, then strain out the ginger and cool completely.
Juice the lemons until you have about ¾ to 1 cup (180–240 ml) of fresh juice. Remove any seeds.
In a large pitcher, combine the pineapple juice, lemon juice, cooled ginger syrup, and 4 cups ice-cold water. Add the fine sea salt and stir well.
Taste and adjust with more syrup or lemon juice only if needed — avoid adding plain sugar directly.
Refrigerate for 1–2 hours until fully cold and flavors are integrated.
Fill glasses with ice, pour over the chilled pineapple lemonade, and garnish with lemon slices and pineapple cubesif desired.
