Bit of uplifting pure substance produced by consumer (4)
I believe the answer is:
user
'consumer' is the definition.
(I know that consumer can be written as user)
'bit of uplifting pure substance produced' is the wordplay.
'uplifting' is a reversal indicator.
'bit of' says the answer is hidden in the clue.
'resu' can be found hidden inside 'pure substance produced'.
'resu' reversed gives 'USER'.
'by' acts as a link.
(Other definitions for user that I've seen before include "Exploiter (of others)" , "With 1a [NEW] he'll need different login" , "junkie" , "Manipulative woman" , "One who works an appliance" .)