To be strictly accurate it's milk (5)
I believe the answer is:
exact
I believe this clue is a double definition.
'to be strictly accurate' is the first definition.
(I've seen this in another clue)
'milk' is the second definition.
(thesaurus)
'it's' acts as a link.
(Other definitions for exact that I've seen before include "Completely accurate" , "Faithful" , "correct in every detail" , "Correct; insist on" , "Demand and obtain" .)