What is the definition of koshu?

Koshu refers specifically to old sake that has been aged. This type of sake undergoes a maturation process, which can significantly alter its characteristics, including flavor, aroma, and color. Aged sake often develops deeper, more complex flavors and can exhibit a smoother mouthfeel compared to freshly brewed sake.

The aging process for koshu may vary in length, with some versions being held for several years, allowing chemical reactions and interactions within the liquid to enhance its profile. The distinction of koshu as aged sake is important in the context of sake tasting and appreciation, as it opens up a different category of flavors and nuances that do not typically appear in younger, freshly brewed sake.

In contrast, the other options refer to sake at varying stages of its production and consumption, not fitting the specific definition of koshu. Freshly brewed sake, for example, represents a very different product that is typically consumed shortly after production. Newly fermented sake involves younger iterations of the brew, while unconsumed sake within a month refers to leftover product rather than a specific category delineated by aging.