American whiskey drinkers can easily locate the proof of their favorite whiskey on the bottle label, but more elusive is its barrel entry proof, the alcohol strength at which it enters the wood barrel. You see, before they dump it into barrels, distillers are legally required to reduce the proof of their bourbon or rye distillate by adding water. Reducing the proof in turn increases the total volume of liquid. Thus, the lower the proof of the whiskey, the more barrels that are required, adding greatly to the final production cost.
In 1962, the U.S. Treasury raised the legal maximum...
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