Where does whiskey’s flavor come from? Around 60% of the flavor comes from the process, but the other 40% comes from the wooden cask (also known as a barrel) that the spirit is made in. Oak is commonly used because it won’t leak but is porous, which lets the whiskey “breathe” oxygen in and out of the barrel.
Barrels can be reused to give a complex flavor to the new liquid. Bourbon and sherry barrels are both commonly used to create whiskey. Some people even argue which is better.
To some, a sherry oak cask is better because the whiskey takes on hints of spice, vanilla, and nutmeg from the barrel. But others prefer how bourbon’s vanilla, caramel, and oak flavors change the whiskey’s flavor profile.
Not only does this process impact the flavor of the whiskey, but it changes its color. For example, red Spanish oak is another wood from which barres are built. It contains tannins that color the final product, making it darker and redder. The more porous the barrel, the more color will be absorbed by the whiskey through the process of evaporation that the porous wood allows.
by 
