When wine keeps cool, it can produce something mellow (8)
I believe the answer is:
clarinet
'something mellow' is the definition.
(instrument known for its mellow sound)
'when wine keeps cool' is the wordplay.
I cannot quite understand how this works, but
'when' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
'cool' could be 'in' (I've seen this in other clues) and 'in' is located in the answer.
The remaining letters 'clart' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'it can produce' is the link.
Can you help me to learn more?
(Other definitions for clarinet that I've seen before include "Single-reed straight-tubed instrument" , "It's for playing" , "Find an instrument in claret" , "Music-maker" , "member of orchestra" .)