Combine the granulated sugar and 1 cup water in a small saucepan. Heat over medium, stirring frequently, until the sugar is fully dissolved and the mixture just comes to a simmer. Do not let it boil vigorously. Remove from heat.

Add flavor components

While the syrup is hot (but off the heat), stir in the caramel color, vanilla extract, citric acid, lime juice, orange oil/extract, lemon oil/extract, ground nutmeg, and ground coriander. Stir thoroughly until evenly incorporated. If using powdered caffeine, sprinkle it in now and stir until dissolved.

Cool and rest

Allow the syrup to cool to room temperature, about 30–45 minutes. Taste and adjust: add up to 1/2 tsp more citric acid for more tang, or a touch more vanilla or orange for sweetness/aroma. Strain through a fine mesh sieve if you used ground spices to remove solids. Refrigerate the finished syrup until cold.

Carbonated Beverage

Chill the carbonated water thoroughly. If you have a soda siphon or carbonator, ensure water is chilled and properly carbonated to a medium-high level.

In a pitcher or directly in serving glasses, add 1/2 cup of the prepared cola syrup per 4 cups of carbonated water (a 1:8 ratio). For a single glass (about 12–16 fl oz), use approximately 2–3 tablespoons of syrup to taste. Gently pour the cold carbonated water over the syrup (or syrup over water) to preserve carbonation.

Stir very gently once or twice to combine without flattening the soda. Add ice if desired—note ice will dilute the drink as it melts.

Garnish & Serve

Pour into glasses over ice if using. Garnish each glass with a lime wedge if desired. Serve immediately while fizzy.