Although the boiling point of essential oil components in various edible spice plants (including the boiling point of star anise oil) is 150-300℃, when their fragrant parts-roots, stems, leaves, flowers, fruits, seeds and barks-are crushed properly, the essential oil and water oozing from the cells and tissues of star anise oil will form multiphase and water. Illicium verum oil is a two-phase mixture that is immiscible with water. The total vapor pressure of immiscible mixture is equal to the sum of vapor pressures of each component. Therefore, when the sum of the vapor pressure of star anise oil and the vapor pressure of water is equal to the pressure in the distillation pot, star anise oil can be distilled together with water vapor at a temperature lower than 100 degrees, which is the basic principle of extracting anise oil essential oil by distillation. It is also the advantage that distillation can extract essential oil at a relatively low temperature.