Wondering if we could get a sticky going in this form to help start off beginners?
Compared with brewing beer, making soda is fast, easy, and cheap. Even a batch from scratch takes only an hour or so to make and can be consumed within 24 hours.
The procedure for making soda is pretty much the same as it is for making beer: heating, cooling, and carbonating. And sanitization is every bit as important as it is for beer.
If you use natural carbonation, bottle and add yeast to start the carbonation process once your soda base is at about room temperature. You can use wine, beer, or Champagne yeast. Wine and champagne yeast strains are generally recommended, because they impart little yeast taste to the finished product. You should use plastic soda bottles. Do not use glass. Should you overcarbonate in glass, you may find yourself with little glass grenades. In addition plastic bottles allow you to "feel" when the carbonation process is finished. When the bottle is rock hard, it is time to refrigerate it to stop the carbonation process.
If you are able, artificial carbonation is the way to go. You get an alcohol-free soda, no yeast at the bottom of the bottle, and no yeast flavor. Use 30 PSI and hook the carbon dioxide to your "out" valve so that the CO2 bubbles through the soda on its way to the top of the keg. (use a smaller diameter 5/16" tube at 20 ft so that it does not foam)
The Ingredients
If you pick up a can or bottle of your favorite commercial soda and read the list of ingredients, you will find that it has four basic elements: water, sweetness, flavor, and acid. You will want the same four basic elements in your homebrewed soda. For sweetness you can use cane sugar and honey. For flavorings you can use anything from a commercial soda flavor to whole ingredients. Lemon juice and citric acid are probably the most accessible sources for the acid component. The acid helps counterbalance the sweetness.
The Easy Method
Your homebrew supply store is likely to have a small selection of soda extracts. You should follow the instructions that come with these extracts. These kits include the extract only, so you will need to supply your own sugar.
The Harder Method
Use a soda base and whole ingredients, such as gingeror other roots, herbs or spices. This is still not very difficult, but you will have to make some decisions about how best to get the flavor from the ingredients.
Choosing Flavor
The sky is the limit when it comes to flavors. Soda makers have made birch and root beer from extract kits; raspberry and cranberry soda using natural fruit extracts; ginger ale, garlic soda, and habañero soda from fresh ingredients; guava soda using a concentrate found in an ethnic market; celery soda from celery seed; and coffee soda from coffee. Cream soda uses vanilla for its flavor. Root beers primary ingredients are wintergreen and sassafras. Real sassafras is carcinogenic, so artificial or natural substitutes for the sassafras flavor are used in all commercial extracts and sodas. The general rule about when to add ingredients is that herbs and spices should be boiled with the soda base, while fruits (including pepper), should be added to the hot base after the boil is finished.
Source: A simplified version of this great article.