The Basics of Distillation

Introduction to an ancient art.

An alembic (from Arabic: الإنبيق, romanized: al-inbīq, 

Distillation is a process of separating and concentrating the components of a liquid mixture. The basic procedure has been practised since the time of the Sumerians of ancient Mesopotamia. As these were the people who also invented beer, it should be no surprise that they also figured out how to make beer even stronger!

Distillation relies for its success on the fact that different compounds in a liquid mixture experience a “phase change” (turning from solid to liquid to vapour) at different temperatures. With a mixture consisting of water and alcohol-related compounds, separating these components can be accomplished in two ways: either freezing the water, or boiling the alcohol.

Freeze distillation, sometimes called “jacking,” relies on the fact that water freezes at a higher temperature than alcohol. While this seems simple enough, in practice it has two major drawbacks. First, it requires a temperature that is much lower than the freezing point of water (-20F or -28C) to get much of an alcohol concentration. This can’t be achieved with a home freezer. More importantly though, freezing and removing the water crystals serves to concentrate not only desirable ethanol, but also fermentation compounds such as methanol, acetone, fusel oils, and other bi-products of yeast fermentation. Drinking a jacked beverage practically ensures a raging hangover as a result.

Heat distillation, in contrast, relies on the fact that the various fermentation components evaporate at a lower temperature than water. It’s also a feasible process for those who live in areas where there are never sub-zero ambient temperatures! In this procedure the liquid mixture is carefully heated in a vessel known as a retort, and the vapours rising from the liquid are directed into a condenser, and from there into a receiver.

To separate the components of a fermentation, the ancients invented “alembic” or “pot-still” distillation, the type of process used to make flavourful spirits from dark sugar solutions, wine, or beer from malted grains. These precursors tend to be low in alcohol, about the same as regular beer or wine (5 to 15 percent alcohol by volume or ABV.) They are first run through the still and all the output is collected in what is called the “stripping run.” This concentrates the ABV to about 30 to 40 percent.

A second “spirit run” concentrates the alcohol further. These various components, or “cuts” are collected separately, and then blended selectively at the distiller’s discretion. As the temperature of the liquid rises, successive compounds begin to evaporate, depending on their boiling point. The first to evaporate, called “foreshots,” are compounds such as acetaldehyde, ethyl acetate, and methyl alcohol. These are not pleasant tasting, and are even poisonous. They are usually discarded.

As the temperature continues to rise, various esters begin to evaporate in a distillation component known as the “heads.” As these tend to be fruity in taste and aroma, they can enhance the flavour of the eventual product, when used judiciously. Knowing how much heads to retain is one of the arts practised by the accomplished distiller.

At about 78C (173F) ethanol, along with some flavour compounds, begins to evaporate into the condenser. This component, known as the “hearts,” becomes the major constituent of the eventual product.

Alemic stills for making Mezcal in Oaxaca, Mexico. Look for "Destillado en Ollas" on the label.
Clay alembic stills for making Mezcal in Oaxaca, Mexico. Look for “Destilado en Ollas” on the label. Source: “Mezcal El Cortador”

Finally, the liquid begins to evaporate its “tails.” Consisting of higher alcohols such as isoaminol and isobutanol, these compounds also carry tastes and aromas we associate with brandy, whisky, and rum distillates. Again, knowing how much of the tails to retain to create complexity and interest in the final product is an art gained by the distiller through experience and sensory awareness.

To make a very pure alcohol such as vodka, a process known as “fractional distillation” is employed. Also called “rectification,” it is used when the liquid components have boiling points that are very close together, such as those in a white sugar wash. The vapours are directed into a tall column where they successively condense, descend, and evaporate again as they rise multiple times, until only a very pure ethanol emerges to be directed into the condenser. In alembic distillation, the distillate must be processed several times to concentrate and purify the product. With fractional distillation the product is purified with only one run through the still.