Why Proof?

By Chris Morris

Why is the measure for the alcoholic strength of a Kentucky Bourbon measured in “proof ”? What does “proof ” mean? Kentucky Bourbon aficionados may be surprised that the rest of the world does not use the term “proof ” when stating the amount of alcohol present in a Whiskey. 

Globally, the percentage or amount of alcohol found in a Whiskey, such as Scotch, is measured in ABV. ABV is the acronym for “alcohol by volume.” That term describes a technical measurement or calculation to determine the percentage of alcohol in the liquid. Here in the United States “proof ” is the old-fashioned term for ABV. Its use goes back to the 18th century when a customer would ask for “proof ” that the whiskey they were buying was of superior quality. 

In those days, the term “superior quality” translated into “Is there a lot of alcohol in this whiskey?” or “Am I getting my money’s worth?” Up until the mid-19th century the determination of proof or alcoholic strength of a spirit was a very inexact measurement. I have experienced this fact firsthand. 

Beginning in 2000, I had the great honor of periodically collaborating with some legendary master distillers over eight years of activities at the George Washington Distillery at Mount Vernon. The reconstruction of this distillery which dated to the 1790s was a project sponsored by Distilled Spirits Council of the United States and Brown-Forman. 

As part of the project, the distillers team followed actual 18th century recipes and processes used then in the handcrafting of Whiskey. Keep in mind the standards of identity that govern our industry today did not exist. One of the recipes we followed was used at George Washington’s distillery by his distiller John Anderson. We learned how our distilling forebearers mashed their grain recipes in small tubs and then subsequently fermented the mash into distiller’s beer in that same vessel. That was a fascinating experience, but most exciting was the fact that we distilled these beers in a small copper pot still over an open fire just as it was done over 200 years ago. 

That still had been crafted by Louisville’s famed Vendome Copper & Brass Works and was a copy of a still owned by the Smithsonian Institution. Allegedly that still was from the original George Washington Distillery. So, a team of experienced distillers from Kentucky who have grown up in the industry and were responsible for crafting some of the world’s iconic Bourbon brands are using 18th century techniques to make Whiskey. We were flabbergasted. How did John Anderson determine when to make his spirit flow cuts, known as the “heads and tails” cuts without modern measuring techniques or equipment? Today the cuts are made at modern distilleries based on several factors, but basically by the alcohol strength of the spirit as it comes off the still. This is measured using various pieces of modern equipment, such as a computerized densimeter or a hydrometer and temperature gauge combination. Since these pieces of equipment were not available to John Anderson in the 1790s, we wondered how we would determine the proper cuts. After some debate and practice it was determined that we would feel the texture of the spirit as it dripped from the still. The heads were thin and watery while the tails were thick and oily. The center, sometimes called “the heart of the run,” seemed to be just right. We were following one of the ways our forebearers judged the quality of the Whiskey, by its “bead” (viscosity). That would not make the cut (no pun intended) technically today but that is what they did. 

Another method I have experimented with is based on historic practice is to mix spirit with gunpowder into a paste and then set it afire. If the combination sparked it meant there was too much water in the spirit. If it burned with a blue flame that meant that there was a higher percentage of alcohol present. Basically, a ratio of 50% water and 50% alcohol is the dividing line for this. So, if you got a blue flame you had “proved” that the spirit was of good versus poor quality. You had “proof ” that the spirit was desirable. These inexact practices are no longer in use today. When did this change and where did the change happen? 

It happened in Woodford County and the mid-19th century at the Old Oscar Pepper distillery, now the home of Woodford Reserve. Master distiller, Dr. James Christopher Crow, introduced the use of the thermometer and hydrometer to accurately measure the amount of alcohol present in his Whiskey. That was an important moment in the development of not only Kentucky Bourbon, but of our industry in general.