According to bottler Kaiyō, mizunara oak casks are the most expensive casks in the world. Japanese oak is hard to maintain: it is porous and it damages easily. And did you know a mizunara oak tree needs to be at least 200 years old before it reaches the proper size to create a cask? Woa! The founder of Kaiyō is skilled in buying quality teaspooned barrels from Japanese distilleries (teaspooning whisky means that the distiller adds a teaspoon of another whisky to their own cask, ensuring that a private bottler can never claim to have bought a cask of single malt whisky. Fun fact!). Must have.