Kentucky has an abundance of water that is filtered through limestone, a process that removes elements that can adversely affect taste. Iron, for example, is filtered out of the water in this way. Next comes mashing, the stage in which the grain and water are cooked. The cooking produces starch, which breaks down to maltose grain sugar. Each distiller then adds the yeast that will convert the sugar to alcohol.
Heat turns the mash into a vapor, which is then cooled to cause condensation.
Finally comes aging, in which wood and the seasons do their work. During summer, the liquid expands into the charred wood, where it gains nuances of flavor and color. In winter, the distillate contracts and rests. The closer to the rooftop, the more intense the heat, which leads to higher alcohol content. After the barrel, bourbon is either blended or bottled directly, all under the scrutiny of the master distiller's carefully trained taste buds.