Although straight Bourbon is typically bottled somewhere between 40% and 45% alcohol, with some reaching to 50%, Bourbon is usually put into the barrel at around 55% to 60% alcohol. (Only a few straight Bourbons exceed the 50% mark. These include: Wild Turkey's "Rare Breed," and Jim Beam's "Booker's" and "Baker's.") When it comes time to bottle the Bourbon, it is dumped from the barrel, usually filtered, and then cut with de-ionized water to bottle strength.

Why, you might ask, do distillers put it in the barrel at a higher proof than they will ultimately bottle at? And the answer is mostly one of economics. Barrels are expensive. The virgin oak of superior quality for barrel-making is itself limited in quantity and expensive. Further, the barrel-making process requires time, care and skill. Hence, oak barrels represent a significant expense for distillers.

Now, a "proof gallon" is a gallon of whiskey at 50% alcohol. And of course it takes one half gallon of alcohol to make up one proof gallon. If you put your whiskey in the barrel at 60% alcohol, then you will get more proof gallons per barrel than if you put it in at, for example, 40% alcohol. So, by aging the whiskey at the higher proof, you can age the same quantity of proof gallons in fewer barrels. And by using fewer barrels, you save money.

But if the distiller tries to age the whiskey at much greater than about 60%, then the flavor changes that maturation produces are diminished and so diluted by the water added before bottling that the whiskey does not contain the desired flavor characteristics. Some Bourbon distilleries, therefore, brag about the relatively lower proof at which their whiskey goes into the barrel.

As for getting whiskey from the wood... The wood of a barrel is relatively dry and porous when the barrel is made. Hence, when the whiskey goes into the barrel, the wood itself absorbs several gallons of spirit. Your typical 53 gallon Bourbon barrel will absorb about two and a half gallons into the wood. When the barrel is emptied ("dumped") those gallons remain in the wood. Of course, that represents lost money to a distiller. So standard practice is to "wash" the barrel. Hot water is sprayed into the barrel and sloshed around, drawing much of the alcohol out of the wood.

How well each barrel is washed out, however, varies, and some Bourbon inevitably remains in the wood.

The practice of putting a few gallons of water into an "empty" barrel, rolling it around of and on for a day or so is called "ponying" a barrel. Ponying a barrel, however, is likely to produce different results from barrel to barrel. For one thing, different barrels are themselves different in flavor -- some sweeter than others, some older than others, etc. And there seems to be some variability in how efficiently the barrels are washed.