American Prohibition ended in 1933, and the subsequent use of bourbon barrels for whiskey manufacturing has changed in the decades since. The use of casks has altered the taste of Scotch whiskey stored in them. This evolution can be seen in the fabrication and use of modern bourbon barrels. The art of crafting bourbon barrels and their predecessors goes back centuries.
The use of whiskey casks goes back a long time, and bourbon barrels have also been use for storage and transport for a wide variety of goods. Ancient Egyptian paintings depict a skill known as coopering, which involves packing and filling these types of wooden barrels. References to coopering have also been found in Celtic and Roman history dating back to the first century A.D.
The word “cooper” derives from the term “cupa,” which is Latin for “vessel.” Three grades of coopering are called wet-, dry-tight and dry coopering. The most skilled coopers engage in wet coopering which involves manufacturing casks that are so air tight as to hold any kind of liquid for transport. Whiskey manufacture alone requires about three million wet coopered wooden casks per year. By the early 19th century, the UK was unable to keep up with the demand for wet coopered casks. Most of the available oak trees has been used for building the Royal Navy’s ships instead.
Distillers in Scotland came to depend more on second-hand whiskey casks by the 17th century. Through various alliances and treaties, Scotland was able to trade for large shipments of wine coming in from London, Bristol, Liverpool and other locations. Mead, port and Madeira were among the most popular wines imported into Scotland. Whiskey distillers then had ready access to a supply of used wine casks to use for storing and transporting their whiskey batches.
Scottish whiskey makers soon found out that the original wine contents of the wooden bourbon barrels had some flavor benefits for the whiskey. Sweeter wines could mellow out whiskey flavors, and it could also mask the taste of whiskey batches that didn’t turn out quite right. Newer whiskey could also be disguised to appear older with some added wine. The most valuable casks were crafted from European oak and found in various geographic locales in central Europe.
The French Navy used the same type of oak for ship-building as well. One ship with a 74-gun capacity took 3,400 oak trees, and the depletion of France’s forests was considerable as a result. By 1669, the French prime minister reorganized the chain of supply for oak. Only the top quality breeds of oak trees were planted, and only the toughest wood was used for building French ships. Napoleon continued the practice by banning all tree felling without prior permission. In 1806, he issued a decree that only oak trees older than 150 years could be cut down. Thanks to Napoleon’s rule, France now has some of the finest oak trees used for barrel coopering. Bourbon barrels became more commonplace later.
George Saintbury once wrote down his observations about the effects of storing whiskey in wine barrels. He noticed that older whiskey batches had darker colors from being kept in casks that once held Madeira or golden sherry. The same whiskey was also sweeter in taste and somewhat heavier in texture.
The introduction of bourbon barrels came with the switch from European to American oak for coopering. Bourbon barrels were made from white or Quercus oak, and many bourbon barrels were made from oak as young as 90 years old. The structure of the wood molecules makes for especially water-tight bourbon barrels. Beginning in the early 20th century, American bourbon barrels became mass produced in factories. Distillers began demanding dark colored bourbon barrels for the effects on whiskey taste. The increase in the use of bourbon barrels only increased after the end of Prohibition.