ラベルには、火入れしてあると記載されていますので、この酸味は杜氏が意図した味なのでしょう。(発酵は既に止まっています。)
I tried "Doburoku", unrefined sake. It was a very sour experience.
This sour taste is probably a chief brewer's intended result, because the label said that this bottle have been heated. (Fermentation was already stopped.)
