Concentrated but failed to keep quiet (9)
I believe the answer is:
distilled
'concentrated' is the definition.
The definition and answer can be both related to change as well as being past participle verbs.
Maybe you can see a link between them that I don't see?
'failed to keep quiet' is the wordplay.
'failed' becomes 'died' ('die' can be a synonym of 'fail').
'to keep' means one lot of letters goes inside another.
'quiet' becomes 'still' (still is a kind of quiet).
'died' enclosing 'still' is 'DISTILLED'.
'but' acts as a link.
Can you help me to learn more?
(Other definitions for distilled that I've seen before include "Brewed" , "produced whisky" .)