Uncrystallised sugar produced by Missouri girls (8)
I believe the answer is:
molasses
'uncrystallised sugar' is the definition.
(juice from sugar)
'by missouri girls' is the wordplay.
'by' is a charade indicator (letters next to each other).
'missouri' becomes 'mo' (abbreviation for the US state).
'girls' becomes 'lasses' (lass can informally mean a girl).
'mo' next to 'lasses' is 'MOLASSES'.
'produced' acts as a link.
(Other definitions for molasses that I've seen before include "Syrupy stuff" , "what refinement can bring" , "Syrup drained from raw sugar for some lass" , "Black treacle" , "Thick dark treacle" .)