Originally Posted by Ducatisti
brewed for 3 days with a Pressure relief valve at top of 3 gallon bottle.
By allowing it to ferment for three days, and letting the pressure out, you will have fermented root beer.
The only reason to use yeast at all is to carbonate the root beer, not to ferment it. By fermenting it, and letting out the c02, you're making an alcoholic beverage and not soda.
Next time, make up a very small batch. Use 1/4 teaspoon of yeast (champagne yeast only) for a 2L size batch. Don't boil or anything, just mix it up. Then pour it into your 2L soda bottle. Cap tightly. When hard, put it in the fridge.
After it's had time to sit in the fridge for two days, pour the soda into a glass, being careful to not resuspend the yeast in the bottom.
There will always be a small amount of alcohol in homemade soda that uses yeast to carbonate. If you are not able to drink any alcohol at all, then you'd need to force carbonate the rootbeer instead of using yeast to carbonate it.