What is the term for the proof at which the spirit is placed into the barrel for aging?

The term that describes the proof at which the spirit is placed into the barrel for aging is known as Entry Proof. This is a critical aspect of bourbon production, as the entry proof can influence the final flavor profile of the bourbon. The spirits are typically diluted to this specific proof before they enter the barrel, ensuring the right balance for interaction with the wood.

Entry Proof is essential because it affects the rate of extraction of flavors and compounds from the barrel. A lower entry proof may result in a more pronounced wood character and sweetness, while a higher proof could intensify the spirit's inherent flavors. Regulations also dictate that for bourbon, the entry proof must not exceed 125 proof (62.5% ABV).

Understanding this concept is crucial for bourbon enthusiasts and professionals alike, as it directly impacts the aging process and the overall quality of the final product. Other terms, like barrel proof or distillation proof, refer to different stages in the whiskey-making process and thus do not denote the same measurement.