This is an adaptation of a cola flavor that has been floating around the web. Most directly it is adapted from the NY Times article found here. They use raw ingredients, but not having access to them at the time, I wanted to do something that incorporated some extracts as well. You'll probably get better flavor with raw ingredients, but you'll also have a little more inconsistency from batch to batch depending on the seasonality of your ingredients.
For lavender I substituted a very floral honey, which seemed to work well for the application. I'll have to hit the health nut store sometime to see if I can pick up some dried flowers in the bulk herb section.
1/4 tsp Nutmeg
1/4 tsp Cinnamon
1/4 tsp Ground Ginger
1-2 drops Pure Anise extract
3 Tbsp floral Honey
1 Tbsp Vanilla extract
1 lb sugar (2 cups)
1 tsp molasses
2 cups water
Top up to 1 gallon with carbonated water.
To begin, zest and juice all three citrus fruits, keep the zest and juice separate. In a saucepan, combine the zests, and the three spices with the 2 cups water. Cover and simmer for 5-10 minutes. Strain out the particulates add the sugar and molasses to the flavor infused water. Heat to dissolve the sugar. Allow to cool and then add the honey, vanilla, anise extract, and citrus juices. Add syrup to carbonated water and there you have homemade cola!
This won't be a direct copy of Coke or Pepsi, because it does not contain the phosphoric acid. If you want a closer match to their cola flavor, there are some places where you can get phosphoric acid, but make sure it is USP or Food Grade. I believe the book Fix the Pumps discusses this somewhat, or the author's website, Art of Drink has some resources available as well, it's not the safest stuff to play with if you don't know what you're doing. Certainly adding some citric acid will help get some extra bite into your cola, but the phosphoric acid is the real deal.