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How does distillation raise the alcohol concentration of a fermented drink?

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distilled spirit The fermentation and distillation process for producing whiskey. The production of whiskey begins with grinding grain into a meal, which is cooked. Malt is introduced to the meal, which results in mash that is cooled and pumped into a fermenter, where yeast is added. The fermented mixture is heated in a still, where the heat vaporizes the alcohol. The alcohol vapours are caught, cooled, condensed, and drawn off as clean, new whiskey. This liquid is stored in a cistern room, and water is added to lower the proof (absolute alcohol content) before the whiskey is placed in new charred oak barrels for aging and later bottling.

Distillation raises the alcohol concentration of a fermented drink by exploiting the difference in boiling points between ethyl alcohol (78.5 °C or 173.3 °F) and water (100 °C or 212 °F).1

Because alcohol has a lower boiling point than water, it vaporizes more readily when the fermented mixture is heated to a temperature above 78.5 °C but below 100 °C. By capturing and cooling these vapors in a condenser, the resulting liquid—or condensate—contains a significantly higher concentration of alcohol than the original mixture.12

This process can be repeated or performed using fractional distillation (rectification) to further purify the spirit and remove unwanted compounds. However, because ethanol and water can form an azeotrope—a mixture that boils at a constant temperature and cannot be separated by simple distillation—there are physical limits to the concentration achievable through conventional methods alone.34