Barrel containing not quite the last bit of bulgur wheat (5)
I believe the answer is:
durum
'bit of bulgur wheat' is the definition.
'durum' can be an answer for 'wheat' (durum wheat is a kind of wheat). I am not sure about the 'bit of bulgur' bit.
'barrel containing not quite the last' is the wordplay.
'barrel' becomes 'drum' (synonyms).
'containing' is an insertion indicator.
'not quite the last' becomes 'u' (I can't justify this - if you can you should give a lot more credence to this answer).
'drum' going around 'u' is 'DURUM'.
Can you help me to learn more?
(Other definitions for durum that I've seen before include "Wheat for pasta flour" , "Type of flour used for pasta" , "Wheat variety" , "Hard type of wheat" , "Kind of wheat used to make pasta" .)