What happens when you combine corn, limestone, white oak, fire, and time? You get one of the best-loved alcoholic spirits in American history: bourbon. Since June 14 is National Bourbon Day, a little history is in order. In the mid-1700s, Scots-Irish settlers in the area that is now Virginia and Kentucky began distilling corn — the only grain native to the area, but one which made for excellent whiskey owing to its sweetness. Another geographical factor was also beneficial to the birth of bourbon.The Limestone Shelf region, where all major American whiskeys are still made today, imbued the local water with calcium while filtering out iron. Turns out that high-calcium, low-iron water is excellent when it comes to makin’ moonshine. We have a clergyman-cum-distiller named Elijah Craig to thank for the third major piece of the bourbon puzzle. In the late 1780s, Craig was using old fish barrels to store his spirits.Not surprisingly, fish-flavored wood did not enhance the whiskey’s taste, so Craig started purifying the white-oak barrels by charring the inside. Then he stamped the barrels with their county of origin (Bourbon County, in his case) and sent them on a 90-day trip down to New Orleans. The charred oak and three-month travel time combined to mellow the whiskey and give it a smooth, smoky, oaky flavor. WhenNew Orleanians requested more of “that whiskey from Bourbon,” the name and the spirit were born.