Look up "Root Beer" in Wikopedia. It has some very interesting information about root beer.
I know that there are root beers that contain alcohol as they are brewed and then carbonated by yeast that consume some of the sugars and give off both alcohol and CO2.
Most comercial root beer is made by adding flavorings and sugar/corn syrup to carbonated water.
The recipe we used for Frosties at a place I worked at after high school was:
200 lbs. sugar, 200 gallons water, 1 gallon root beer concentrate. Mix into root beer syrup and add 15 milliliters of syrup to 12 oz. carbonated water.
For me, A & W root beer tastes very similar to birch beer, and has a distinctly wintergreen flavor with a sweetness derived from sugar and mollases. I have duplicated this flavor in my home, just to see if I could do it. But it's much easier to pruchase in a store.
It's interesting to note that A&W, and IBC root meers are both manufacture by Cadbury/Schwepps. Also, from the Wikepedia article, you will discover that there are a host of possible ingredients, which explains why one brand of root beer tastes so very different from another.
For instance, I love Frosty Root Beer, but detest Hire's Root Beer. One of my best freinds is exactly the opposite. He love Hire's and doesn't like A&W.
In any case, I can't drink the wonderfull concoction any more, except as diet root beer due to diabetes.
Seeeeeya; Goodweed of the North