Poor menials must eat old wheat concoction (8)
I believe the answer is:
semolina
'wheat concoction' is the definition.
(wheat product)
'poor menials must eat old' is the wordplay.
'poor' indicates anagramming the letters.
'must eat' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'menials' anagrammed gives 'semlina'.
'semlina' going around 'o' is 'SEMOLINA'.
(Other definitions for semolina that I've seen before include "Lemon is a strange pasta" , "Wheat food found in a soil, men" , "pudding ingredient" , "Milled wheat product" , "sweet" .)