What defines the proof level of a spirit before it is barreled for aging?

The proof level of a spirit before it is barreled for aging is defined as the entry proof. This term refers to the specific alcohol content of the spirit at the time it is placed in the barrel for maturation. Entry proof is significant because it can influence the aging process, affecting how the spirit interacts with the wood of the barrel and ultimately impacts flavor development.

Maintaining a consistent entry proof is essential for producers as it can affect not only the characteristics of the bourbon as it matures but also the regulatory aspects concerning labeling and classification. The entry proof typically varies based on the distiller's preferences and the style of whiskey they aim to produce, which adds an additional layer of complexity to the craft of bourbon making.

Initial proof and final proof refer to the spirit's proof before distillation and after aging, respectively, while barrel leaf is not a recognized term within this context. Understanding these definitions helps clarify the critical stages in the production of bourbon and the importance of entry proof in shaping the final product.