Walk into any decent whiskey shop and you'll see both terms on labels. They sound like they mean the same thing. They don't — and the difference matters if you're chasing high-proof expressions.

Barrel Proof (a.k.a. Cask Strength)

Barrel proof means the bourbon was bottled without dilution — whatever proof it was when the barrel was dumped is the proof in the bottle. No water added, no blending to hit a target number.

Because of Kentucky's climate, barrels breathe hard through summer heat and winter cold. Over years of that cycling, water evaporates faster than alcohol. A bourbon entered at 125 proof can exit the barrel at 130, 140, even higher depending on the warehouse location and age. So barrel proof bottlings are often — though not always — higher than the legal entry proof ceiling.

The key: the bottling proof reflects what aging did to the spirit. It's a snapshot of the barrel at dump time.

Examples: Stagg, Booker's, Wild Turkey Rare Breed.

Full Proof

Full proof is a term coined — and trademarked — by Buffalo Trace Distillery. It means something more specific: the bourbon is bottled at the same proof it entered the barrel. Not the proof it exited. The entry proof.

So if a bourbon went into the barrel at 125 proof, a full proof bottling comes out at 125 proof — regardless of what happened inside the barrel over the years. The distiller adds water (or doesn't) to hit that original entry number.

It's a nod to the old pre-Prohibition practice of bottling at barrel entry proof — a way of connecting the final product back to its starting point.

Examples: Blanton's Full Proof, E.H. Taylor Full Proof.

Why the Distinction Matters

Both are undiluted in spirit (pun intended), but they measure different things:

• Barrel proof = proof at exit. Reflects what aging did to the spirit.
• Full proof = proof at entry. A fixed reference point, independent of aging.

In practice, full proof bottlings may actually be lower proof than true barrel proof expressions, since the barrel typically gains proof during Kentucky aging. Neither is inherently stronger or better — they're just different ways of thinking about what "uncut" means.

If you want to understand what determines where these numbers start, take a look at barrel entry proof — it's the foundation both concepts build on.