Alcohol Distillation and the Sense of Smell

Fermentation produces 75% water and alcohol by weight – both without flavor. The remaining 25% consists of various chemical compounds like acids, aldehydes and esters (collectively known as congeners) that give alcoholic beverages their unique flavors both good and bad.

Distillers use stills to separate congeners from ethanol by heating alcohol-containing liquid until it vaporizes, then moving it along its swan neck or lyne arm until reaching a condenser which returns it as liquid distillate with significantly increased alcohol concentration than originally.

Distillers then test its alcohol content and purity to see if it meets their desired levels, repeating the process to increase concentration levels as needed before aging and reaching proof levels necessary for specific styles of spirits.

The hearts are composed of mostly ethanol and are generally free of off-tasting congeners such as toxic methanol, acetaldehyde (a key contributor to hangovers), or paint thinner-smelling acetone. One of the skills of distilling lies in knowing when and where to cut off heads from hearts – thus increasing ethanol percentage while decreasing congener proportion.

As the alcoholic strength of the hearts decreases, the run passes into tails – less alcoholic by volume and developing distinctive flavors such as wet cardboard or old towels. Some distillers choose to discard this part of their run while others redirect it for redistillation or use as fuel for their still. Ester oils with fruity or floral odors may also be found here.