It's instrumental in coral gas production (3,7)
I believe the answer is:
cor anglais
'it's instrumental' is the definition.
(cor anglais is a kind of musical instrument)
'in coral gas production' is the wordplay.
'production' is an anagram indicator.
'in'+'coral'+'gas'='incoralgas'
'incoralgas' anagrammed gives 'COR ANGLAIS'.
(Other definitions for cor anglais that I've seen before include "Woodwind instrument" , "MUSICAL INSTRUMENT" , "belonging to a broken-down 27 [CARTHORSE]" , "Orchestra member rarely" , "alto member of family" .)