Stir together 186 g lemon juice, 375 g orange juice, and 100 g granulated sugar in a bowl until the sugar dissolves. Cover and chill in the refrigerator for 2 hours.
Pour the chilled syrup through a fine-mesh sieve into a clean punch bowl or large jug.
Add 6 piece chopped pineapple, 1000 g soda water, and 1000 g ginger ale, stirring gently to combine. Serve chilled over crushed ice.
For 100 g orange juice, use about 30 g lemon juice mixed with 70 g water and sugar to taste. It is much sharper and lacks orange aroma; add sugar gradually.
For 100 g orange juice, use about 30 g lime juice with 70 g water and sugar to taste. It is more floral and acidic; reduce other souring agents in the dish.
Use the same weight. Stir in 1 tsp grated fresh ginger and a pinch of sugar per 200 ml for a ginger-fizzy effect; it will be less sweet and less ale-like.
Steep 5 g crushed fresh ginger in hot water, strain, cool and top up with soda water. Use in place of the same weight of ginger ale; sharper and not sweet.