The boiling, condensing, and subsequent return to the boiler of a volatile liquid. It is used to enhance the separation of liquids of differing volatilities as in the process of distillation. In a distillation column used to separate volatile liquids by virtue of their differing boiling points, using more reflux decreases the number of plates required for the separation. Conversely, using less reflux increases the number of plates required. The reflux ratio is the ratio of distillate taken from the distillation process to the reflux returned as liquid for further separation. Where no distillate is taken, the process operates on total reflux. The minimum reflux ratio corresponds to an infinite number of trays to bring about a separation. Ideally, the reflux ratio should be optimal for which the combined fixed costs and the cost of operation should be least.