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On the Subject of Bourbon Whiskey: Charring Oak Barrels was no Accident – it was Science

This post was written by Michelle Cadoree Bradley, a Science Reference Specialist in the Science, Technology and Business Division.

In a previous post I alluded to writing an additional Bourbon-related post. This follow-up looks at a century of early scientific advancements and the impact on bourbon distillation in America.

Figure 1: Eli Barnum & Benj. Brooks Still Design Patent, 1808. Records of the Patent and Trademark Office, National Archives Identifier 305887.

We shall bend science “to the useful purposes of life” in the domestic arts, vowed Thomas Jefferson in an 1804 letter to Michael Krafft, the author of The American Distiller.
(Papers of Thomas Jefferson. Volume 43: 11 March to 30 June 1804, James P. Maclure.)

Krafft had written to Jefferson introducing himself and his new publication on distilling, in which Krafft wished to include a dedication to Jefferson and which was to be the first work on distillation published in America. When Jefferson sold his collection to the Library of Congress, it contained Krafft’s work, along with other English and French works on brewing and distilling. Distillation had long been a home practice by colonials, but scientific study of the process and technological improvements in stills began to move distillation from cookery to industry.

By the early 1800s the burgeoning science of preservation was being applied to liquor and spirits. 

In a November 1806 article “On the means of preserving water in long sea voyages, and the application of the same means for keeping wines,” in the Journal of Natural Philosophy Chemistry and the Arts, author M. L. G. advises that “The process of carbonizing the inner surface of casks may also afford advantages for the preservation of wines… conjecture that it would become still more agreeable if preserved in casks charred within … Casks which have received this preparation may be used for all the purposes in which liquids are to be preserved.” (v. 15, p. 225-228)

In the article “Discovery and Improvements in arts and manufactures in 1806” in the January 1807 The Atheneum reporting on preservation of water at sea, noted that “Charring is much recommended for wine-casks also, and all casks which are to contain liquors,” after reports that Captain Krusenstern, who commanded the Russian expedition of discovery in 1805, found that charring the insides of casks proved “the great efficacy which the operation of charring the insides of casks has to preserve water.”

Not only a means of preservation, early chemists had already noted that storage in oak casks for French Brandy imparted color and improved the flavor of that liquor, such so that they were already devising ways of imparting the “oaky” characteristics to other liquors.

Figure 2: Pre-title page insert from Harrison Hall’s The Distiller, 1818.

The Complete Distiller (A. Cooper, London, various editions) advised as early as 1757 that “the mighty secret; the ingredient from whence the French brandy acquires it’s colour” came from its oak cask.  Tests to determine if brandy were genuine, which were carried out by applying a tincture in a test amount, reacted because of the oak. Soon distillers knew that for their counterfeit brandy to pass as real all they had to do was add oak shavings to it. Further to imitate the color of French Brandy one had only to know that the color was produced by it “laying long in the cask.”   In a Dictionary of Chemistry, the article on alcohol informs that distillers wishing to impart an amber color to the liquor (and to imitate popular French brandy) proposed “oak casks” because in oak casks it “soon acquires an amber colour, a peculiar flavor, and something like an unctuosity of consistence… the English distiller imitates by design these accidental qualities. The most obvious and natural method of doing this would be by impregnating a pure spirit with the extractive, resinous, and colouring matter of oak …”.

By 1809 distillation was ready to take on a distinctly American swagger, as suggested in Samuel McHarry’s  rather lengthy book sub-title — The practical distiller, or, An introduction to making whiskey, gin, brandy, spirits, &c. &c. of better quality and in larger quantities than produced by the present mode of distilling, from the produce of the United States, such as rye, corn, buck-wheat, apples, peaches, potatoes, pumpions, and turnips: with directions how to conduct and improve the practical part of distilling in all its branches: together with directions for purifying, clearing, and colouring whiskey, making spirits similar to French brandy, &c. from the spirits of rye, corn, apples, potatoes, &c. &c., and sundry extracts of approved receipts for making cider, domestic wines, and beer.  A mere decade later Harrison Hall’s publication The Distiller already listed more than 80 American patents relating to distilling, such as that by Eli Barnum found in the records of the Patent and Trademark Office in the U. S.  National Archives.

By the end of the 19th century the processes of making bourbon and the use of oak, particularly charred oak barrels, were inseparable. 

The “bourbon barrel” was a known part of the distillation process with even cooperages making barrels expressly for the use of bourbon as indicated in an article in The Wood-Worker. (“Cooperage. Some questions and answers.” v. 19, no. 12, Feb. 1896, p. 30-31). It quotes that for “bourbon” barrels “… the process of manufacture is essentially the same as the manufacture of other barrels, except the barrel is not steamed and is charred thoroughly on the inside by burning when being fired…This is done that the tannic acid may be brought to the inside surface of the staves and cause the goods to color rapidly.”

The beginning of the century saw Jefferson’s thoughts on bending science to “useful purpose” in industry brought full forward in the application of the scientific process to the study of the maturation of whiskies. 

In 1907 the Internal Revenue Service published a study begun in 1898, on the effects of maturation in oak casks on whiskey.  This 8-year scientific study began with whiskeys supplied by whiskey distillers, who furnished products stored in “new, charred, oak barrels”. Referring to the barrels by the term “charred package” which they described as “a barrel, the staves of which have been charred on the inside more or less deeply by the action of fire. The charring of barrels in which whiskey is to be stored” and which was in “almost universal practice” in America. The study by C. A. Crampton and L.M. Tolman published in the 1907 Journal of the American Chemical Society (v. 30, no. 1: 98-136) concluded what everyone already knew–that the characteristic of American whiskey was derived from the charred barrels in which it is aged.

BFU: Inspired by Ben Franklin

This post was written by Kelsey Diemand Librarian in Residence in the Science, Technology and Business Division. You may know Benjamin Franklin as a scientist and inventor, statesman and diplomat, or maybe you recognize him as the guy on the one-hundred dollar bill. Ben Franklin is famous for his role in the American Enlightenment and […]