Due to its many essential qualities in barrel making, the main wood used in cooperages is oak, especially for spirit and eaux-de vie maturation as well as whisky maturation. Other than its mechanical properties (strength), it also has excellent thermal insulation and remarkable watertightness. Oak growth depends on multiple factors (genetics, geography, climate), that consequently affects the grain size and chemical composition. Depending on the growth conditions, the heartwood (or perfect wood) of the three main oak species used in cooperages (Quercus petraea, Quercus robur, and Quercus alba) has a specific polymer structure and specific aromatic molecules, that will influence the aromatic quality and sensory characteristics of whiskies aged in barrels that are revealed during tasting. 

Whether it is for the creation of single malts or blended whiskies, each distillery will choose their barrels depending on the aromas to achieve during maturation and sought after by connoisseurs: coconut aromas and smoothness for American whiskies (Bourbon), finesse and balance for Japanese whiskies, roundness, complexity, and fruity aromas for Scotch whiskies.