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Distilling

Charles Phypers Using a Hydrometer, circa 1972; 96.X1.13.

Once the fermentation process was completed and the available sugars converted to alcohol by the yeast, the separation of alcohol from the fermented mash was achieved by distilling. The fermented mash was heated in a still, which caused the alcohol to vaporize and rise to the top where it was condensed and collected in a receiving tank. The product of this process was heavy in flavour and was kept for blending purposes. To produce a lighter, or base whisky, this product underwent further distillation.

In secondary distillation, many of the heavy flavouring components, or congeners, were removed and the final product was high in alcoholic strength with a delicate flavour and aroma. During this process, the heavy whiskies were heated and the vapours passed through a distillation column. Since the various flavour components boil at different temperatures, these fractions separated out along the column. The low-boiling (more volatile) compounds - aldehydes and esters - came off first and were collected by the stillman as the "heads". The part known as the "centres" came off next to become the base whisky. The final portion contains the higher boiling components (mostly fusel oils) and was removed as the "tails."

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