Moonshine stills were historically used for the fermentation of corn into alcohol for drinking, especially during the time of Prohibition during the 1920s. Corn, malt and yeast were mixed into a mash and heated to ferment and evaporate alcohol, which then was condensed for later use.
The traditional moonshine mash recipe called for corn and malt, the latter of which is necessary to convert the corn into sugar. This sugar is metabolized by yeast into alcohol, a process known as fermentation.
After the yeast converts the sugar into alcohol, adding heat evaporates the alcohol from the mash. Since alcohol has a lower boiling point than water, it is possible to separate it from the mash and water in this way. This process is known as distillation, and it is from this term that the name still is derived. Many moonshiners used propane for heating the mash to start the distillation process.
The evaporated alcohol sometimes still contains pieces of the mash as it evaporates and is forced through a pipe out of the still. Most stills incorporated a keg to re-evaporate the alcohol and filter out these particles, but this was not strictly necessary. The final stage of using a still involved cooling the alcohol vapor in a coiled metal pipe called the worm, usually with running water from a nearby creek.