How does steam distillation separate water-immiscible substances?

Steam distillation is a specialized technique used to separate and purify substances that are immiscible (incapable of mixing) and chemically nonreactive with water.1

The process works by introducing a current of steam directly into the mixture within a still. This serves two primary purposes:12
* Lowering the Boiling Point: By introducing steam, the substance can be distilled at a temperature lower than its normal boiling point. This is particularly beneficial for materials that might decompose if heated to their standard boiling temperatures under atmospheric pressure.1
* Vaporization and Transport: The steam provides the necessary heat to cause the evaporation of the volatile components. As the steam and the vaporized substance travel together, they are subsequently condensed into an aqueous distillate.12

Because the substance is immiscible with water, the resulting condensate typically forms two distinct layers, allowing for easy separation of the desired organic liquid from the water and any nonvolatile impurities. Common applications include the processing of fatty acids and various oils.21