In practice, almost all bourbons marketed today are made from more than two-thirds corn, have been aged at least four years, and do qualify as "straight bourbon"—with or without the "straight bourbon" label. The exceptions are inexpensive commodity brands of bourbon aged only three years and pre-mixed cocktails made with bourbon aged the minimum two years.
This spirit is placed in charred oak barrels for aging, which is what imparts color. Consequently, bourbons that have been aged longer are generally darker in color.
After aging, bourbon is withdrawn from the barrel, diluted with water and bottled. Bottling proof must be at least 80 proof (40% abv) and most whiskey is sold at 80 proof. Other common proofs are 86, 90, 94, 100 and 107, and whiskeys of up to 151 proof have been sold. Some higher proof bottlings are "barrel proof," meaning that they have not been diluted after removal from the barrels.
The Kentucky Bourbon Trail is a patchwork of paths that lead to eight well-known distilleries: Buffalo Trace (Frankfort, the oldest continually operating distillery in the United States), Four Roses (Lawrenceburg), Heaven Hill (Bardstown), Jim Beam (Clermont), Maker's Mark (Loretto), Tom Moore (Bardstown, producer of the 1792 brand, added to the trail on August 27, 2008), Wild Turkey (Lawrenceburg), and Woodford Reserve (Versailles).
Although the invention of bourbon has often been attributed to a Baptist minister and distiller named Elijah Craig, there is no evidence supporting this assertion. As with most innovations, there may have been no single "inventor" of bourbon, which evolved into its present form only in the late 19th century.
Distilling probably came to what became Kentucky when European-American, and particularly Scottish and Ulster Scots, settlement began in earnest in the late 18th century. The spirit they made evolved and gained a name in the early 19th century.
When American pioneers pushed west of the Allegheny Mountains following the American Revolution, the first counties they founded covered vast regions. One of these original, huge counties was Bourbon, established in 1785 and named after the French royal family. While this vast county was being carved into many smaller ones, early in the 19th century, many people continued to call the region Old Bourbon. Located within Old Bourbon was the principal Ohio River port from which whiskey and other products were shipped. "Old Bourbon" was stencilled on the barrels to indicate their port of origin. Old Bourbon whiskey was different because it was the first corn whiskey most people had ever tasted. In time, bourbon became the name for any corn-based whiskey.
A refinement variously credited to either Dr. James C. Crow or Dr. Jason S. Amburgey was the sour mash process, by which each new fermentation is conditioned with some amount of spent mash (previously fermented mash that has been separated from its alcohol). (Spent mash is also known as distillers' spent grain, stillage, and slop or feed mash, so named because it is used as animal feed.) The acid introduced by using the sour mash controls the growth of bacteria that could taint the whiskey and creates a proper pH balance for the yeast to work.
As of 2005, all straight bourbons use a sour mash process. Dr. Crow or Dr. Amburgey developed this refinement while working at the Old Oscar Pepper Distillery (now the Woodford Reserve Distillery) in Woodford County, Kentucky. As of today, there are no running distilleries within the current boundaries of Bourbon County due to new counties being formed from Bourbon County over time.
A resolution of the U.S. Congress in 1964 declared bourbon to be a "distinctive product of the United States." That resolution asked "the appropriate agencies of the United States Government . . . [to] take appropriate action to prohibit importation into the United States of whiskey designated as 'Bourbon Whiskey.'" Federal regulation now defines "bourbon whiskey" to only include "bourbon" produced in the United States.
Since 2003, high-end bourbons have seen revenue grow from $450 million to over $500 million (£231 million to over £257 million or €308 million to over €343 million), some 2.2 million cases, in the United States. High-end bourbon sales accounted for eight percent of total spirits growth in 2006. Most high-end bourbons are aged for six years or longer.
In 2007, United States spirits exports, virtually all of which are American whiskey, exceeded $1 billion for the first time. This represents a 15 percent increase over 2006. American whiskey is now sold in more than 100 different countries. The leading markets are the United Kingdom, Canada, Germany, Australia, and Japan. Key emerging markets for American whiskey are China, Vietnam, Brazil, Chile, Romania, and Bulgaria.