Even novice enthusiasts of whiskey will know that their beloved drink is produced through distillation. But what exactly is distillation? What happens inside those beautifully crafted pots or complex columns? And what role does distillation play in shaping the distinctive character of distilled spirits?
Distillation relies on a simple principle: different molecules have different boiling points. For example, ethanol boils at around 172 degrees Fahrenheit, while water boils at 212 degrees Fahrenheit. If you have a solution consisting of various molecules with different boiling points, you can use distillation to separate those components by capturing the vapor generated from boiling the liquid.
Take Scotch whisky as an example. The wash (which is the fermented liquid made from barley, water, and yeast) poured into the still contains only about 8% alcohol, more or less—similar to the strength of an after-work beer. However, whisky, as we know, is much stronger than that.
To increase the alcohol concentration, distillers heat the wash in the pot of their stills. Eventually, the wash begins to steam. Since alcohol has a lower boiling point than water, the resulting steam has a higher alcohol concentration than the wash. In the case of Scotch and Irish whiskey (or any pot-distilled whiskey), the vapor travels up the swan neck (or lyne arm) of the still, passes over the top, and encounters a condenser. The condenser turns it back into a liquid, known as a distillate, which then exits the still through the spirit safe.
That’s the basic principle, and it applies to other types of distilled spirits such as rum, brandy, and tequila. However, things can become more complex depending on the distillation process, the method used, and, of course, the art of distilling itself.
HEADS, HEARTS, AND TAILS
It’s important to remember that the alcohol concentration in the vapor is not uniform. Instead, it varies. The first vapors to emerge from the wash have the highest alcohol content. Over time, this concentration gradually decreases until it reaches zero.
To account for this variation, distillers divide the spirit stream into fractions by making cuts. The initial part of the distillation, known as the heads, is the strongest. However, along with ethyl alcohol (the desirable component), the heads also contain toxic and volatile compounds like methanol and acetone. Additionally, they have a distinct odor resembling nail polish remover. Therefore, distillers separate the heads and usually recycle them into the next batch for re-distillation.
Next comes the desirable part of the distillation: the hearts. This section still contains a significant amount of alcohol, but it also possesses a favorable taste, often reflecting the raw ingredient being distilled. The hearts are collected in a special tank and later transferred into barrels.
Eventually, the alcohol strength further decreases, marking the beginning of the tails. This final part of the distillation has a lower alcohol content by volume and starts to develop heavy, pungent flavors like wet cardboard and old towels. However, similar to the heads, most distillers redirect the tails to the next batch for redistillation in order to avoid wasting any alcohol.
Determining precisely when to make these cuts is one of the most critical decisions a distiller faces. While guidelines exist, there are no rigid rules. Distillers rely on their past experience, their senses, their artistry, and their intuition to make the correct cuts that will establish the foundation for the final flavor profile.
ACE copper column still
Most American whiskeys like bourbon and rye, along with many rums, vodkas, and tequilas, are actually produced using column stills—a type of equipment famously associated with Irish inventor Aeneas Coffey, who patented a version of it in 1830. Unlike the batch system of pot still distillation, Coffey’s still allowed continuous operation, making it more efficient.
In modern large-scale bourbon stills, the process operates similarly, relying on steam heat to continuously separate a fermented mash into fractions. These stills consist of a column filled with multiple chambers containing porous barriers (either sieve trays or bubble cap trays, depending on the style and location within the column). The fermented wash is piped into the column approximately two-thirds of the way up, while steam is piped into the bottom.
As the steam passes through the wash, the wash begins to boil. The alcoholic vapor rises through the column, condensing and re-vaporizing each time it encounters one of the trays, becoming increasingly concentrated in alcohol with each chamber. Instead of making cuts over time, the still allows distillers to extract their desired fraction from the column while removing the spent mash.
Most whiskeys are made using column stills simply because they are the most common type in the United States. However, we also appreciate a well-made pot still whiskey, and many of our rums are produced using pot stills. These two methods are just different ways to create exceptional spirits.