To be leg­ally sold, Calvados must be at least 40% abv. This alco­hol con­tent is obtained by the gradu­al addi­tion of dis­tilled or demin­er­al­ised water to the eau-de-vie. This is known as reduction.How­ever, some “cask strength” Calvados are unre­duced. They have a “nat­ur­al” alco­hol con­tent cre­ated by the evap­or­a­tion of the eau-de-vie over time. Taken dir­ectly from the top of the barrel, they are usu­ally bottled on demand and show a won­der­ful con­cen­tra­tion of aromas. Some “cask strength” Calvados can con­tain up to 55% vol.