6 cups white sugar
3 1/3 gallons cold water
1 (2 ounce) bottle root beer extract
4 pounds dry ice
In a large cooler, mix together the sugar and water, stirring to dissolve sugar completely. Stir in the root beer extract. Carefully place the dry ice into the cooler, and cover loosely with the lid. Do not secure the lid, as pressure may build up.
Let the mixture brew for about an hour before serving. Leftover root beer can be stored in one gallon milk jugs.