LIMESTONE WATER AND THE ORIGIN OF BOURBON

Bourbon whiskey, which is made from fermented corn mash aged in charred oak barrels, is a uniquely American spirit produced almost exclusively in Kentucky. Exports of bourbon totaled more than $700 million in 2007. Its distinctive taste has traditionally been attributed in part to the “limestone water” used in its production. Given the prevalence of carbonate rocks, corn cultivation, and alcohol consumption throughout much of North America and indeed the world, why did bourbon originate in Kentucky, and what roles has water actually played in its history? Addressing these questions requires a consideration of settlement patterns and practices and the characteristics of water in karst terrains.

European immigrants, in whose cultures alcohol production and consumption were ingrained, began moving beyond the Appalachians in the latter half of the 18th century. Thousands of settlers were drawn to the Bluegrass region of north-central Kentucky, which is marked by fertile residual soils developed on limestone bedrock. Corn was readily cultivated and its distillation provided a high-value product that would not spoil. Consequently, production of whiskey commenced there as early as 1776. Many farms and settlements were located near perennial springs in the Bluegrass region. These springs were valuable not only because of a year-round supply of water, but also because their relatively uniform, cool temperature (~14 to 15 C) facilitated condensation of steam during distillation. Moreover, shallow groundwater and streams in the region typically have dilute, Ca-Mg-bicarbonate-type compositions with circumneutral pH, which limits dissolved Fe and promotes growth of bacteria involved in fermentation.

The production of bourbon became standardized and industrial in the first half of the 19th century. Because of the relatively low yield of springs in the Bluegrass region, most distilleries now rely on treated stream water, but some smaller distilleries still use groundwater. Regardless of the exact source of water, its role in the taste of bourbon combines terroir and craft through the growing of grain, fermentation, and distilling.