Over the decades, oak barrels have proven to be the supreme vehicles for aging potable liquors. This is due to its semi-permeable nature that allows the alcohol and water to diffuse through the thickness of the walls of oak barrels, thereby STAVE promoting minimum evaporation within the wood surface to the level of 2 percent per year in Scotland. This provides the very slow maturation process that is so vital to a high-quality final product. Traditionally, Scotch whisky is not aged in NEW oak barrels, as are Brandies (Spanish and Cognac) and Bourbon. Historically, these liquors have benefited from the newer oak barrels. The CARAMEL bitterness associated with new oak barrels results from excessive LIGNIS, PHENOLS, TANNINS, and RESINSm which are very rarely present in and unappreciated by aged malt whisky connoisseurs.
Two types of white oak are used to fashion Spanish or American oak barrels. AMERICAN oak barrels (Quercus ALBA) contains less than one-half the entire wood extract found in the EUROPEAN oak barrels (Quercus ROBUR). The bourbon whiskey industry relies solely on American oak barrels that have been properly charred in order to foster the carmelisation of wood sugars that are so vital to bourbon’s final character. This pre-treatment of American oak barrels with fire and spirit has become acceptable to Scottish distillers. The alternative and highly-coveted source of pre-used cask is JEREZ Spain, which offers both European and American oak barrels that have previously held SHERRY wines.
As with everything else in life, it will be appreciated that the expected improvement of spirit quality within the cask does not always manifest and those SULLIED oak barrels are discarded, regardless of how minor their imperfection(s) may be. A similarity between CORKS in whisky or win and wood for casks does exist, so that the SOURISH MUSTY-DANK flavours of bad wood ruins the entire content of oak barrels.