A reflux still is a type of still used for distillation, which is a process of separating components of a mixture based on their boiling points. In a reflux still, the vapor produced by heating the mixture is condensed and returned to the still, where it is further heated and condensed again. This repeated process of condensation and vaporization, also known as refluxing, helps to separate the components of the mixture more effectively.

The reflux still consists of a vertical column that is packed with material, such as copper mesh or ceramic beads, that provides a large surface area for condensation and helps to increase the purity of the distillate. The mixture to be distilled is heated at the bottom of the column, and the vapor rises up through the column, where it is cooled and condensed by a water-cooled condenser at the top of the column.

Some reflux stills also have a fractionating column, which is a series of plates or trays that help to further separate the components of the mixture by allowing them to condense and vaporize on each plate or tray. This results in a higher degree of separation and a more pure distillate.

Reflux stills are commonly used to produce high-proof alcohol, such as whiskey or vodka, as well as for other applications, such as extracting essential oils from plants or purifying water.