Made from Kentucky and Indiana corn, selected rye, and superior malted barley, all bourbon produced by Buffalo Trace Distillery is aged in century-old warehouses. Constructed of massive wood beams and covered by a brick shell, these structures allow the alternating cooling and warming of Kentucky's four distinct seasons to mature the bourbon by nature's timetable. Steam pumped throughout the warehouses during the extreme cold of winter compensates for the dramatic drops in temperature and gives the whiskey additional cycles in and out of the wood. This is said to make for a more balanced bourbon as the liquid is able to take additional advantage of the natural sugars occurring in the charred barrels. The distillery was the first to use this method of aging in 1859 and has been doing so ever since.