Step #1
"Soften" your yeast by dissolving in a cup of lukewarm (body temperature) water for 5 - 15 minutes. This should be thoroughly mixed up before adding to the rest of the ingredients. For best results, use fresh champagne or beer yeast. If you're in doubt about the freshness of the yeast, do not use it! Bread yeast will make your soft drinks taste "yeasty" or "bready."
Step #2
Shake extract bottle well. Combine extract with sugar and lukewarm water. At this point you may wish to "play" with the recipe by increasing the amount of extract or sugar per gallon. Adjust the proportions to taste. However, the one critical proportion is the amount of yeast per gallon. Do not exceed the recommended amounts!
Step #3
Now mix the "yeast slurry" with the extract/sugar water. This should be stirred thoroughly to insure that the yeast is evenly dispersed throughout the beverage. Otherwise, some bottles may carbonate very rapidly while others take considerably longer.
Step #4
Sanitize your bottles. Use either: 1 oz. unscented bleach per gallon water for 10 minutes or 2 capfuls of iodophor per 5 gallons for 5 minutes. Note: bottles must be clean before sanitizing. Unless you have some reason to suspect the quality of your tap water, we recommended giving the bottles a quick rinse with warm to hot tap water after sanitation. Now fill your bottles, leaving 1 - 2 inches of headspace in each bottle. Seal with caps.
Step #5
Age soda at room temperature for 3 - 4 days before cooling. You may wish to "check" the carbonation level before proceeding. This can be done by simply chilling a bottle and sampling. An alternative is to bottle at least some soda in re-used plastic 16 - 67 oz. PET commercial soda bottles and screwing the cap back on. When your homemade soda becomes carbonated, these plastic bottles become very hard. Under any circumstances, as soon as your homemade soda is carbonated, it must be refrigerated! Otherwise, it will gush upon opening (at best) or it may even explode! For best results, age the soda in the refrigerator for 1 - 2 weeks. This will allow the flavors to meld and the yeast sediment to firmly pack down on the bottom of the bottles. This slight yeast deposit is a natural result of the fermentation process and is not harmful in any way, but some people find the flavor objectionable. For this reason, it is best to pour carefully out of the bottle so as to leave most of the yeast deposit behind. Again, for best results, refrigerate your soda prior to opening.
Amount to be Made Yeast Amount Extract (or to suit taste) --Sugar --(or to suit taste) Water
1 gallon 1/8 tsp. 1 TBS. (1/2 oz.) or 2 TBS. Zatarain's 2 cups (~1 lb.)
fill to 1 gallon
2 gallons 1/4 tsp 2 TBS. (1 oz.) or 2 oz. Zatarain's
4 cups (~2 lb.)
fill to 2 gallon or 2 1/2 gallons for Zatarain's
4 gallons 1/2tsp. 2 oz. or 4 oz. Zatarain's 8 cups (~4 lb.)
fill to 4 gallon or 5 gallons for Zatarain's
* Please note that Zatarain's Root Beer extract uses 4 oz. extract for 5 gallons soda. For a heavenly variation on root beer, add a tablespoon of vanilla extract along with the root beer extract.  Also, note that some customers have had very good results with adding 8 oz. of malto-dextrin to the mix to enhance the body & mouthfeel.