Writer wasted, but not with form of consumption (6)
I believe the answer is:
nibble
'form of consumption' is the definition.
(I know that nibble is a type of bite)
'writer wasted but not with' is the wordplay.
'writer' becomes 'nib' (something which writes).
'wasted' becomes 'blew' (eg to blow money is to waste it).
'but not' suggests deleting specific letters.
'with' becomes 'w' (abbreviation).
'blew' with 'w' taken away is 'ble'.
'nib'+'ble'='NIBBLE'
(Other definitions for nibble that I've seen before include "Bite gently and eat a little at a time" , "Take small bites of" , "Take tiny bites" , "Bite off very small pieces" , "Snack" .)