Recipe from Double the Deliciousnes
For 5 gallons:
5 pounds of sugar
5 gallons of water
1 large jar of Rootbeer extract (I think it was 2.5 ounces)
5 pounds dry ice
Mix sugar with about half the water until sugar is dissolved. (If you use all the water you will most likely not have a spoon long enough to reach the bottom!) Fill with the rest of the water. Add the rootbeer extract and stir to combine. Put in the dry ice & watch it "smoke"!
Set lid on top of cooler...don't screw on tight, you need to let the "smoke" escape a little.
So, if you noticed the ingredients they are pretty easy to down-size, just in case you don't need 5 gallons of rootbeer!:) If you want 3 gallons, use 3 gallons or water, 3 pounds of sugar, 3 pounds of dry ice & 3/5th's of the rootbeer extract. (I know that ones a little hard to measure, but you can always just use your taste buds as well...try it and see if it needs more flavor!)
So for 1 gallon it's 1 gallon water, 1 pound sugar, 1 pound dry ice, and 1/5th of the rootbeer extract.