Single malt whisky (and sometimes a third) time. The final spirit, called "new make spirit", generally has an alcohol content of 60 to 70%. Most new-make malt whisky is diluted to about 62.5% a.b.v. before it is placed in casks to mature. The "new-make spirit", or unaged whisky, is then placed in oak casks to mature. By law, all Scotch whisky must be aged for a minimum of three years in oak casks, though many single malts are matured for much longer. The whisky continues to develop and change as it spends time in the wood, and maturation periods of twenty years or
Barrel the much lower cost. Sherry is stored in casks made of North American oak, which is slightly more porous than French or Spanish oak. The casks, or butts, are filled five-sixths full, leaving "the space of two fists" empty at the top to allow flor to develop on top of the wine. Sherry is also commonly swapped between barrels of different ages, a process that is known as Solera. Laws in several jurisdictions require that whisky be aged in wooden barrels. The law in the United States requires that "straight whisky" (with the exception of corn whisky) must be stored