If using invert sugar for smoother mouthfeel, make 200 ml: combine 200 g granulated sugar and 100 ml water in a small saucepan. Heat gently, stirring until sugar dissolves. Add 1/8 tsp cream of tartar or 1 tsp lemon juice, simmer 5–10 minutes, then cool. Alternatively use 200 ml simple syrup (1:1).

Measure 200 ml of your prepared invert or simple syrup into a clean measuring cup. Add 10 ml caramel color syrup and stir to combine. Set aside.

Make cola flavor blend

Combine the flavor oils and extracts: in a small glass container, add 2 ml orange oil, 1 ml lemon oil, 0.5 ml lime oil, 0.2 ml nutmeg oil, 0.2 ml cinnamon oil, 0.1 ml cassia or cinnamon leaf (if using), and 2 ml vanilla extract. Add 6 ml cold water to help dilute and form a small emulsion. Mix vigorously or vortex until uniform. This yields approximately 12 ml of cola flavor concentrate.

Taste the concentrate carefully (very small amount). Adjust by adding up to 0.5 ml more orange or vanilla if you prefer a sweeter aroma, or tiny increments of citrus oil for brightness. Keep total volume near 12 ml.

Acid, caffeine and final blending

In a large clean 2.5–3 L pitcher or bottle, pour 2 liters of chilled carbonated water. For best fizz retention, use cold water and work quickly.

Add the 200 ml sweetener + caramel mixture to the carbonated water. Pour slowly down the side to reduce excessive foaming.

Stir gently with a long spoon 6–8 strokes to incorporate sweetener without flattening the carbonation.

Add the 12 ml cola flavor blend (prepare as above) to the mixture. Again stir gently 6–8 strokes to incorporate.

Add 2 tsp phosphoric acid solution (or 1 tsp citric acid powder dissolved in a little water) and 0.5 tsp caffeine solution if using. Stir gently to distribute. These adjust acidity and bitterness to resemble cola. Taste cautiously — acids are potent; adjust in 0.25 tsp increments if needed.

If you notice excessive frothing or loss of carbonation, stop stirring and let bubbles settle; avoid vigorous shaking. Cap the bottle or cover the pitcher and chill thoroughly for at least 1 hour before serving to let flavors meld.

Serve

Pour over ice if desired. Garnish with lemon or lime slices. Store refrigerated in a sealed container and consume within 3–5 days for best flavor and fizz.