Combine granulated sugar, dark brown sugar and 1 cup water in a small saucepan. Heat over medium, stirring until all sugar dissolves and mixture reaches a gentle simmer. Remove from heat.

Color and cool

Stir in 2 tablespoons caramel color until evenly combined. Allow the syrup to cool to warm (about 10–15 minutes).

Add flavorings

Once slightly cooled, whisk in fresh lime juice, vanilla extract, orange oil, lemon oil, ground cinnamon, ground nutmeg and ground coriander (or their extracts/oils). If using powdered caffeine, dissolve a very small pinch into a teaspoon of warm syrup first, then stir into the batch. Taste and adjust: increase lime for brightness or vanilla for roundness, but add oils/extracts very sparingly — they are highly concentrated.

Strain and rest

If you used any ground spices, strain the syrup through a fine mesh sieve or cheesecloth into a clean jar to remove solids. Seal and refrigerate the concentrate if not using immediately. The concentrate will keep 1–2 weeks refrigerated.

Assemble Coca‑Cola

Fill a tall glass with ice (about 2 cups).

Pour 1/2 cup (120 ml) cold carbonated water into the glass.

Add 2 tablespoons of the prepared syrup concentrate to the carbonated water. Stir gently once or twice to combine. Taste and adjust syrup to water ratio to preference (typical range 1.5–3 tablespoons syrup per 4–6 oz of sparkling water).

Top with the remaining carbonated water to reach about 4 cups total liquid in a pitcher (if making multiple servings) or leave as-is for a single serving. Stir gently to preserve carbonation.

Garnish with a lime wedge and an orange peel twist if desired. Serve immediately while cold and fizzy.