Once opened, sake oxidizes but fortunately more slowly than wine.
See Also
Top 8 Tips on How to Drink Sake the Right Way | Roka AkorDo You Know Where the 12 Strongest Liquors in the World Come From?The Best Six Sakes for Any Price PointHow Many Beers Equal A Shot?Drink sake within one week of opening but the most pleasurable state of the sake will be in the first 3 days.
Unopened, sake is best drunk within 12 months of the bottling date or 2 years if kept in cool storage/refrigerated. Of course this time is way shorter for Nama (unpasteurized sake) or if the storage area gets warm. The cooler temperatures will slow down maturation.
