Temperature right in old Spanish kingdom to produce aromatic herb (8)
I believe the answer is:
tarragon
'aromatic herb' is the definition.
(I've seen this before)
'temperature right in old spanish kingdom' is the wordplay.
'temperature' becomes 't' (abbreviation).
'right' becomes 'r' (common abbreviation).
'in' is an insertion indicator.
'old spanish kingdom' becomes 'aragon' (I've seen this before).
'r' put inside 'aragon' is 'arragon'.
't'+'arragon'='TARRAGON'
'to produce' is the link.
(Other definitions for tarragon that I've seen before include "Herb - a torn rag (anag)" , "Herb coming" , "Arrogant sort of herb" , "Aromatic herb used in cooking" , "cooking ingredient" .)