In September I visited the Jim Beam and Maker's Mark distilleries as part of the Kentucky Bourbon Festival. For all the distilleries I've been to in 10 different countries, I'd never seen a bourbon distillery.
The Claremont Jim Beam distillery is a huge facility, and one of two where the product is distilled. They receive tons of grain daily, and distill whiskey 24 hours a day, 6 days each week. The annual output is around 6 million cases of bourbon each year. (I believe they also distill the small batch bourbon collection here- Booker's, Baker's, Knob Creek, and Basil Hayden.) Beam uses 70 warehouses to store their 1.7-1.8 million barrels of bourbon that are aging.
Beam is made from corn, rye, and barley. Interestingly, we get GMO corn in the US bourbon, but they distill, age, and bottle non-GMO spirit separately for export to Europe where they have restrictions against GMO products. (I definitely want to learn more about this so if anyone has a non-hysterical GMO book/video they can recommend let me know.)
The bourbon is first column distilled in the "beer still" that's about six stories high. It is then distilled a second time in the "doubler" which they say looks like a pot still but is continuous. (We didn't see it.)
The barrel warehouses are not only enormous, they're very tall- nine stories, with each story holding three tiers of barrels. At the top of the warehouse where it's hot, the barrels gain proof over time as more water evaporates out of the barrel (through the wood) than spirit. At the bottom of the warehouse, the whiskey loses proof as more alcohol evaporates than water.
When selecting barrels to use for Beam, they take barrels from each level of the warehouse to make up the final blend. For the Booker's bottling, which is cask-strength and unfiltered, they only take barrels from one middle floor.