Zest one orange to yield about 1 tsp zest. In a small heatproof bowl, combine the granulated sugar and hot water (about 2 tablespoons just off the boil). Stir until the sugar fully dissolves to make a quick syrup.

In a measuring cup or small pitcher, combine 1 cup fresh orange juice and 1 tablespoon fresh lemon juice. Stir in the orange zest and the warm simple syrup until fully incorporated. If using orange extract, add 1 tsp now; if using citric acid for extra tang, dissolve it into the juice mixture a little at a time and taste to reach desired brightness (start with 1/4 tsp).

Taste the concentrate: it should be brighter and slightly sweeter than plain juice because carbonation will mute flavors. Adjust sweetness by adding up to 1 tablespoon more sugar dissolved into a teaspoon of warm water, or add more lemon/citric acid for acidity.

Carbonation & Finishing

Chill: Ensure the club soda or sparkling water is well chilled. Cold liquids retain carbonation better and produce a crisper soda.

Assemble the Fanta-style orange soda

Fill a tall glass with about 1/2 cup (about 1/2 the glass) of ice cubes. Pour 1/4 cup (60 ml) of the orange concentrate over the ice (adjust depending on how strong/sweet you want the flavor). Slowly top with 1/2 cup (120 ml) chilled club soda, pouring gently down the side to preserve bubbles. Stir very gently once to combine. For a single serving, a typical ratio is 1 part concentrate to 2–3 parts soda; scale quantities if making multiple servings.

Garnish & serve: Add an orange slice to the rim or float it on top. Serve immediately to enjoy maximum carbonation. If preparing a pitcher, mix the full concentrate with the chilled sparkling water just before serving and pour over ice.