Key to dire concoction - removed moisture (5)
I believe the answer is:
dried
'removed moisture' is the definition.
(I've seen this in another clue)
'key to dire concoction' is the wordplay.
'key' becomes 'd' (musical key).
'concoction' indicates anagramming the letters.
'dire' anagrammed gives 'ried'.
'd'+'ried'='DRIED'
(Other definitions for dried that I've seen before include "Desiccated" , "Parched" , "Like clean dishes" , "Preserved, in a way" , "dehydrated" .)