Krug uses small 205-litre oak casks tailor-made from trees that are more than two centuries old in the forests of Hautes Futaies in Central France. Krug never use these casks immediately; during the first two or three years, they receive only second and third grape juices, with the goal of "tanning" the casks through the fermentation process, ridding them naturally of their woody aromas, making them well-seasoned and organoleptically inert. The average age of Krug oak casks is 20 years. They are retired after approximately 40 years of use.