An alcohol molecule is large..........and a water molecule is small

• Since a water molecule is very small, it is easier for it to escape through the barrel than the much larger alcohol molecule.Because the atmosphere at the top of a Rickhouse is very hot and dry, the water molecules escape much faster than the alcohol molecules thus driving the proof UP in those barrels also concentrating the flavors. Think of the top floors of a Rickhouse like your attic. On a summer day when it's 90 degrees outside, it's way over 100 degrees in your attic. Most straight whiskies are entered in the barrel at 125 proof. So the proof will rise every year, and after 10 years of aging can rise as high as 150 or more, and I've personally seen and tasted whiskey at 160 proof from the very top tier.
  
• As a result, barrels at the top of a Rickhouse age at an accelerated pace.
  
• Conversely the atmosphere at the bottom of the Rickhouse is moist and cool.Since a water molecule is very small, water can penetrate the barrel from the surrounding moisture and that drives the proof DOWN in those barrels. On that same summer day when your attic is way over 100 degrees, it will be moist and cool in your basement, more like 75 degrees.
  
• Barrels at the bottom of a Rickhouse age at a slower pace, and the flavors are not as pronounced. Barrels from the middle of the Rickhouses more mimic what's going on outside. The barrels down here go from 125 proof, down to below 110 proof. I've seen them as low as 107.
  
• There's also air flow to consider here and that helps in the aging process and control the atmosphere inside each Rickhouse.
  
• The middle of the Rickhouse or "Center Cut", the barrels start and end around 125 proof.
  

• With 3 barrels on each floor, you can easily see by this diagram that bourbons age differently all through the house, and even sitting next to each other. Those barrels in the middle of the Rickhouse are further away from the sun, as those on the outside that are more effected by the sun shining on the sides. So it really showcases how a Single Barrel Bourbon will taste a little different from barrel to barrel.
  
• If you mingle several barrels together from different floors, and inside and out as in a Small Batch Bourbon, then that product will taste more consistent from bottle to bottle, and batch to batch.
  
• Main line bourbons like Evan Williams, Jim Beam, Wild Turkey, and Jack Daniels are from a larger number of barrels collected from all areas of the Rickhouse.
  
• Small Batch and Single Barrel Bourbons generally come from more specific areas of the Rickhouses, and in either one Single Barrel, or a dump of a lesser number of barrels for a Small Batch.
  
• Different distilleries define Small Batch differently, so keep that in mind with # of barrels in a dump or areas of Rickhouses, or specific Rickhouses themselves as the Small Batch.