Gather ingredients: water, brown sugar or white sugar, root beer extract, yeast, and optional vanilla
Sanitize a large pot, funnel, bottles, and caps
Heat some of the water and dissolve the sugar
Add the remaining water and let the mixture cool to room temperature
Stir in root beer extract and optional vanilla
Add a small amount of yeast
Fill clean plastic or pressure-safe bottles, leaving some headspace
Cap the bottles loosely or use swing-top bottles
Let the bottles sit at room temperature for 12 to 48 hours
Check carbonation by gently squeezing plastic bottles or testing one bottle
Move the bottles to the refrigerator when carbonation is reached
Chill before opening
Open carefully and serve cold