by In the PourLast Updated: 09/08/2017
Making a distilled spirit consists of 3 main phases: Fermentation, Distilling, and Finishing.
Alcoholic fermentation is the conversion of sugar into alcohol by yeast.
The first thing that’s needed is a source of sugar. Historically this has been the cheapest excess crop in the region (for example, corn in the US, or barley in Scotland). The ingredients are typically prepared by boiling them into a mash which releases starch into sugars that yeast can consume. Technically sugar water can be used instead, but it is more expensive and less flavorful than a mash of agricultural products.
After the ferment is prepared, yeast are added to produce alcohol. Yeast are microscopic organisms in the fungus family and consist of many different species and strains. Some distillers use wild yeast, but many have a proprietary strain. Yeast consume glucose sugar and excrete ethanol alcohol and carbon dioxide. After fermenting to between 10-20% abv, they go dormant and sink to the bottom of the mash.
Distillation captures alcohol by boiling it into a steam and then condensing it back into a liquid.
After fermentation, the mash (now called the wash) is transferred to a kettle to be distilled. The kettle is gradually heated and the wash begins to evaporate. Since alcohol is a volatile molecule, it has a low boiling point (78.37°C) and it evaporates at a much higher rate than water and other less volatile chemicals. The steam flows through a condenser where it is cooled and turns back into a liquid. After most of the alcohol has been collected, distillation is ceased and the remaining wash is discarded.
A Pot Still a traditional design used for hundreds of years. Its shape causes other fermentation byproducts (called congeners) to be included along with the alcohol and water. All congeners are impurities, but some contribute positively to flavor (especially when aged) while others are undesirable. Distillation is an art as much as a science, and much of the art involves developing a method to optimize the mix of congeners in the final product. Pot stills are typically used to make rich and flavorful spirits like whiskey, rum, and brandy.
Column Stills, on the other hand, are a modern design. They are engineered specifically to distill a highly pure product. As the vapor rises in the column, the impurities cool down enough to cause them to condense and “rain” back down into the kettle. Since pure alcohol has a relatively low boiling point, it can proceed out of the column to the condenser for collection. Designing such a still requires a good knowledge of physics to calculate the optimal column height. Column stills are typically used to make clear and neutral spirits such as vodka or gin.
After distillation, a spirit may be processed further to enhance its flavor and taste. The most common finishing processes are Aging and Infusing.
Aging is typically done in charred wooden casks. There are many factors involved with the aging process including: duration, type of wood, level of char, and climate. It is a very complicated process and master distillers keep extensive notes on every barrel as it ages. All else being equal, the longer a spirit ages the darker it becomes. However the other factors are very important; for example, most Scotch is older yet lighter than most Bourbon.
Infusing involves subjecting the spirit to fruits, herbs, or other botanicals. Alcohol is a strong solvent which makes it ideal for extracting flavors. Many commercial liqueurs are infused with various flavors, but the process can be done at home as well.