How should I prepare kola nuts for creating a soft drink? I have recently gotten into making my own soft drinks, and I would like to attempt making a cola.   I found an online spice retailer that sells Kola Nut and bought some, but I have no real idea how to prepare them for use.   I also don't know how much I should use for a liter or two of soda, but I can figure that out via experimentation if I have to.

But what should I do with the kola nuts?   Do they need to be ground before I boil them in a simple syrup, or should the pieces just be dropped in as-is?   How much time does it take to extract the flavor from them?

Edit:  I have made my own ginger ale using fresh ginger and my own berry soda using a bag of frozen berries, and I am a homebrewer and have a kegging system and a carbonator cap for soda bottles.   I really just want to know if there are special considerations for how to treat kola nuts.
There are several cola recipes on this site.
Recipe 2.6 references a kola extract recipe from the following book: Food Flavourings, by Joseph Merory, AVI Publishing Company, 1960.

I'd assume that the kola nuts are added as in pieces, similar to how they are consumed - Kola nuts are consumed by breaking them open and into pieces.