We are often taught in high school that mixtures of liquids with different boiling points can be separated by distillation, and that is obviously true, the nuances are skipped for the sake of simplicity. The reality is that a complex mixture, especially ones containing water and other polar compounds like ethanol does not separate cleanly due to a number of factors, hydrogen bonding being a key one.
THE MANUFACTURE OF SCOTCH GRAIN WHISKY
By Magnus Pyke, B.Sc, Ph.D., F.R.I.C., F.R.S.E. (The Distillers Company Ltd., Glenochil Research Station, Menstrie,
The Institute of Brewing & Distilling Received 10/A October, 1064