As the title suggests, I am wondering how do we describe food which has gone stale or food that has gone cold after being left out there for too long? I checked jisho and 大辞林 but I did not manage to find anything conclusive. Thanks for any help!
For food that has gone cold (doesn't need to be so cold, but like coffee that is not hot enough anymore) you use 冷める, so in most cases a structure like 冷めてしまったスープ works best.
I am not a native English speaker (either), so I don't fully understand "gone stale", but I think there are many different ways to describe food that are no longer in their optimum state. E.g. for noodles that have swollen when kept too long in the soup, you use "ラーメンが伸びた". For bread that became hard,かたくなった, for vegetables くさった etc.