Distillation is the process of separating mixtures based on the differences in their volatilities in a boiling liquid mixture. It is a unit operation, or a physical separation process, and not a chemical reaction. Distillation has been used for a variety of purposes since at least 1st Century AD. Not surprisingly, I’ll be focusing on the production of the alcoholic beverage in this discussion.
Alcohol can be made from a variety of agricultural products using a basic three-step sequence:
1. The feed-stock (the raw material) is broken down chemically, usually through cooking or the addition of enzymes.
2. Fermentation, i.e., the action of micro-organisms (usually yeast) to produce a “beer” (The term “beer” describes the liquid traction of a fermented mixture of water and ground or crushed grain that is usually no more than 6-10% alcohol, hence the similarity of the process and the final alcohol content to that of domestic beer.) containing a small percentage of alcohol. In addition to alcohol, the mixture contains the remains of the feedstock, the yeast cells and various other substances dissolved in water.
3. Separating the alcohol from the water and other components in the beer, by distillation, to obtain the alcohol in a purer form.
Since the first two steps in the distilling process are the same as the steps for brewing beer, I will begin by describing the process for brewing a stout similar to Guinness. Then, since the initial ingredients in the two beverages are strikingly similar, I will process to describe the distillation of a whiskey similar to Bushmills. And so we begin.
First, we must break down the raw material (this is actually a fairly simple process). We begin by taking some barley and malting it. What is malting? Malting is the process of allowing a grain to germinate (or sprout) and then halting that process. This develops the enzymes required to modify the grain’s starches into sugars, including monosaccharides (glucose, fructose, etc.) and disaccharides (sucrose, maltose, etc.). It also develops other enzymes, such as proteases, which break down the proteins in the grain into forms that can be utilized by yeast.
After the grains are malted, we must grind them into a very rough flour, often called grist. An important part of the milling of the grains is the retention of the grain’s husk. This allows the mash of converted grain to create a filter bed during lautering, which we will get to in a moment.
Now that we have milled grain, we place it into a container called a Mash Tun and add water at a specified temperature. This is where science comes into play. Some brewers/distillers use a single temperature of water (usually around 152°F) and infuse the mash for 60-90 min. Then the grains are drained (or lautered) and rinsed with hotter water (170°F) to ensure that all of the sugars are rinsed out of the grains. This is called a single-infusion mash. Others take a more complex approach where water is added at around 104°F and allowed to sit for twenty minutes. This process is repeated at temperatures of 122°F, 144°F, and 162°F. This is called multi-step or decoction mashing. The more complex mashing is often utilized because at each temperature different enzymes are released and as these enzymes are released, they break down different forms of sugars, proteins, and starches. Every brewery and distillery has their own system and fine tunes the temperatures at which they mash. Once the mashing is complete, the liquid (now called wort) is drained, cooled, and sent to the next part of the process.
Fermentation is a simple, yet crucial part of the entire process. We place the wort into a container and add yeast. After a few hours, the yeast starts to feed on the sugars present in the liquid. As the yeast consumes the sugars, it releases carbon dioxide, and more importantly, alcohol. This process can take as little as 56 hours, or as long as 4 days. After fermentation is complete, the process for beer and spirits depart from one another.
Before we go on, a quick note about yeast: Distillers typically use distillers yeast, while brewers, use a host of strains, each contributing to the flavor of the individual beers. Many breweries have their own secret strands of yeast.
Following the fermentation process, beer is often aged, sometimes for months, and then carbonated in kegs, bottles or cans, either by natural carbonation using small amounts of yeast, or artificial carbonation using co2, nitrogen, or a combination of the two. From there it makes its way to distributors, then stores and finally to your home where you enjoy it.
Spirits on the other hand, must be distilled following the fermentation process. From the fermentor, we must pump the liquid into either a pot or a column still. Once in the still, we heat the liquid. Since alcohol and water have separate boiling temperatures, the alcohol begins to vaporize before the water. Alcohol vapors travel up the neck of the still and down into a condensing tube that is usually cooled by water. There, the vapors are then turned back into a liquid and we drain the alcohol out. The crucial part of the distillation process is when the alcohol starts to flow out of the condenser, in addition to the alcohol, the first and last parts of the distillate usually contain unwanted contaminants. A good distiller knows the right points to “cut” the spirit in order to obtain only the best of the run without wasting valuable spirit. Good spirits result not from the number of distillations, but from the quality of the distillations.
From the still, we place the spirit into wooden barrels for aging, and after a predetermined amount of time, smooth whiskey is brought forth from the cask, bottled, and enjoyed by people around the world. Cheers!