HOW DOES DISTILLING ALCOHOL WORK?
Have you ever gazed at a bottle of bourbon or rye and wondered, “How exactly do distillers make this stuff?” It’s a good question. Unlike making wine or beer, distilled spirits aren’t really something you can experiment with as a DIY project. Not only are they complicated and expensive to make, but it’s also illegal to distill at home in the United States.
Every distillery’s process is a little bit different, but underneath all that variety, the principles underpinning the distilling process are the same everywhere. Here’s a brief primer on how distilling alcohol works, including fermentation and distillation.
It’s easiest to explain distillation with an example. Let’s take single malt Scotch whisky, as its production process is relatively simple. (The same general process also applies to pot distilled Irish whiskey, American whiskey, and other pot distilled whiskies around the world.)
The first step in making Scotch whisky is to create a fermented liquid made from malted barley, yeast, and water called wash. Distillers start by steeping the malt in hot water to extract its carbohydrates and turn them into sweet sugars. Then they add yeast, which transforms those sugars into alcohol. Whiskey always begins with grain, but anything with starch and/or sugar can be fermented, from sugarcane juice or grape juice, to agave hearts or potatoes.
Whisky wash is about as alcoholic as a strong beer, usually somewhere between seven and nine percent alcohol by volume. But unlike beer, it’s neither hoppy nor carbonated–plus, it’s usually unfiltered and frequently sour, making it a pretty unappetizing pint. Fortunately, it’s destined for greater things.
Scotch whisky is made using pot distillation, which uses a pot still that looks a little like an enormous, oddly shaped tea kettle. Once wash is pumped into the base of the still, electric heaters start to warm it up.
Just like when you’re making tea or heating soup, as the heat increases, vapors rise. But (in an important difference between distillation and soup-making) alcohol boils at a lower temperature than water. That means the first vapors that begin to emerge are stronger in alcohol than the wash as a whole.
Those alcohol vapors travel up into the neck of the still. Along the way, they might re-condense on the wall of the still (especially if they encounter any impediments, like odd curves or areas that are intentionally cooled), then re-vaporize when the temperature rises again. Eventually, the lightest vapors will pass over the neck of the still into a near-horizontal portion called a lyne arm, where they eventually encounter a condenser that transforms them from a gas back into a liquid.
This liquid is called a distillate, and it’s what ultimately exits the still at the other end. Because of the various boiling points of different compounds in the wash, the character of the distillate changes over the course of the distillation run. For this reason, distillers make “cuts,” or separate the distillate stream into three sections called the head, heart, and tail.
The hearts, as you might guess, is the good stuff: strong in alcohol, rich in flavor, yet free from the volatile and/or funky compounds found in the heads and tails. In the case of Scotch whisky, the hearts get filled into oak barrels, aged for several years, and ultimately released as a delicious final product.
But even though the heads and tails aren’t desirable, they’re thrown out. (There’s valuable alcohol in there, after all!) Instead, they’re recycled into the next batch, and the whole process begins again.
BEYOND POT DISTILLATION
Pot stills are just one of the many still types used in distillation. Column stills, which are often associated with Irish inventor Aeneas Coffey, who held a patent on an early version, can be run continuously, which means they’re more efficient. Lots of different configurations mean they can be tuned to make super-pure neutral grain spirits, or hugely flavorful bourbons or rums. And hybrid stills are a combination of the two, pairing the enhanced efficiency of column stills with the hands-on batch process of pot stills.
Most of Barrell Craft Spirits’ small-batch bourbons, ryes, and American whiskeys were distilled on column stills, as they’re the most common type in the bourbon industry. Many of our small batch rums were made on pot stills. And some of our signature releases like Armida, Seagrass, and Dovetail rely on spirits distilled in multiple different ways. Want to taste for yourself? Shop online on our website or use our map tool to find a retailer near you.