Vacuum distillation

From theEthanolSource.com

Vacuum distillation is the practice of boiling liquids in an atmosphere that has less pressure than the atmosphere. This is done by using a vacuum source (pump or venturi) to lower the pressure within the vessel containing the fluids to be separated. As the pressure is reduced, one of the fluids will begin to boil. This happens due to the fact that boiling is a function of vapor pressure and temperature. We can boil a liquid either by heating it or by lowering the pressure. As we lower the pressure in the vessel, the temperature at which the phase change from a liquid to a gas is also lowered.

For example:

Water boils at 100 degrees C and a pressure of 1 atmosphere. Under a vacuum, water will boil at skin temperature. This is the basis for a glass novelty toy. In this toy a small glass vessel has a dip tube that reaches almost to the bottom of the vessel and connects to a vessel several inches above the bottom one with curves in the glass above the lower vessel. The bottom vessel is partially filled with a red liquid. When the toy is held on the palm, or encased by the hand, water in the lower vessel boils, increasing the pressure in the vessel and forcing fluid up the dip tube and into a higher vessel.

Since ethanol boils before water, reducing the pressure above the tank makes it so that the alcohol can be separated at a much lower temperature.