After the distillation and doubler processes, the bourbon is proofed down to a barrel entry proof of 107. This is done by adding water to the bourbon, reducing the alcohol content to the desired level before it is aged in barrels. The choice of a low barrel entry proof can have an impact on the aging process and the flavors that develop over time.
It's worth mentioning that the proof of the bourbon can also change over time during the aging process. As the bourbon interacts with the wood of the barrels, it undergoes evaporation and absorption, leading to a gradual reduction in proof. This is commonly referred to as the “angel's share” and can contribute to the complexity and concentration of flavors in the bourbon.