To make a still, you need to be able to heat fermented corn mash to its boiling point of 77.8 degrees C but not to 100 degrees C, which is the boiling point for water. In this way you can separate the alcohol from the water and all the other contaminates that are in the corn mash. You need to do this in a sealed system so that you can collect the steam from the corn mash and condense it back into a liquid away from the undesirable parts of the corn mash.
Drill a hole in the top of the keg with a 1/4-inch drill bit and drill, just next to the tapping cap. Use a reciprocating saw with a metal blade to saw the tapping cap out at the hole; cut as close to the cap as possible. Pull the tapping cap and the centre tube from the keg.
Place a 1.5-inch rubber stopper in the hole to see if it will be the right fit. Press it in tightly, but keep it so that you can remove it. Remove the cap and drill two holes into the top of it, one hole with a 1/8-inch drill bit and one with a 1/4-inch drill bit.
Coil the middle 7 feet of a 9-foot piece of 1/4-inch copper tubing around a glass bottle, leaving 1 foot on either side straight. Take your time to ensure that the coils will all be uniform and there will be no corners in which liquid can get trapped.
Place a meat thermometer into the 1/8-inch hole and one end of the copper tubing into the 1/4-inch hole. Go around the holes in the stopper with caulk to form a tight seal.
Use the 1/4-inch drill bit to drill a hole in a glass carboy with cap. Place the other end of the copper tubing into the hole and caulk it to make a good seal. Place the carboy on the ground and replace the cap.
Set the keg on a campfire stand over some campfire wood. Fill the keg with fermented corn mash and use a rubber mallet to stop the hole with the rubber stopper. Put some caulk around the edges of the stopper to make a tight fit and give it about an hour to dry.
Light the fire underneath the keg and keep the temperature inside the keg above 77.8 degrees C, but below 100 degrees C so that the alcohol will evaporate into the copper tubing, where it will condense into liquid and run into the carboy, but the water will not evaporate.
Mix the liquid that you get in the carboy with the drink of your choice before drinking it. It will have a powerful and bitter taste.
Keep the carboy away from the fire while distilling the corn mash.