Foodstuff in steam on large overturned barrel (8)
I believe the answer is:
hazelnut
'foodstuff' is the definition.
(hazelnuts are food)
'steam on large overturned barrel' is the wordplay.
'steam' becomes 'haze' (both can mean a mist).
'on' says to put letters next to each other.
'large' becomes 'L' (eg in clothes sizes).
'overturned' says the letters should be written backwards.
'barrel' becomes 'tun' (tun is a kind of barrel).
'tun' backwards is 'nut'.
'haze'+'l'+'nut'='HAZELNUT'
'in' acts as a link.
(Other definitions for hazelnut that I've seen before include "Filbert or cob" , "Cobnut or filbert" .)