Caustic soda, or sodium hydroxide, is a common commercial cleaning product, which turns certain substances, including grease, fats, oils, and proteins into a water soluble material. Caustic sodas are generally used for heavy duty cleaning projects, such as clogged drains, storage equipment and preparation machines. Cleaning a beer keg with caustic soda will remove materials built up over time from the brewing process and storage. Caustic soda is highly corrosive so proper safety measures should be taken to avoid contact with skin or eyes, as well as inhalation or ingestion.

Fill a large saucepan with lukewarm water. Add enough water to fill your keg about three-quarters full. The water should be between 80 to 100 degrees Fahrenheit.

Place the saucepan on a burner and turn it on to medium heat. Allow the water to heat for about five minutes. Place the metal stirrer in the pan and begin stirring in long, slow strokes.

Calculate how much caustic soda to add to the mixture by multiplying the amount of water you're using by the percentage of soda you want the mixture to be. A caustic soda mixture of between 20 to 50 percent is best for cleaning. For instance, if you are using 15 gallons of water, multiply 15 by 20 percent to get the amount of caustic soda to add.

Begin adding the caustic soda flakes or pellets to the heating water by adding a few cups at a time, while constantly stirring the mixture. Add all the caustic soda to the water, slowly stirring. Once all the soda has been added, remove the saucepan from the heat and allow it to cool slightly.

Disassemble all exterior pieces from the keg including the tap, O ring and lid. The tap and O ring can be soaked in leftover caustic soda solution or be cleaned with warm, soapy water.

Fill the keg with the caustic soda solution and replace the lid. Allow the keg to sit with the solution for about 30 minutes.

Flip the keg over so it is standing on its lid and allow it to sit like this for another 30 minutes.

Remove the lid and scrub the sides and bottom of the keg with a metal brush. Scrub the keg lid with a metal brush as well. Caustic soda will turn any residual soda or grease into a water soluble material which can be easily removed with a brush.

Drain the caustic soda from the keg; then fill the keg with water and agitate it with the brush for several minutes. Drain the water. Repeat this three or four times to guarantee all the soda has been rinsed from the keg. Rinse the lid, tap and O ring thoroughly several times, then reattach to the keg.