Most awful kind of wine consumed by Den (8)
I believe the answer is:
nastiest
'most awful' is the definition.
('nasty' can be similar in meaning to 'awful')
'kind of wine consumed by den' is the wordplay.
'kind of wine' becomes 'asti'.
'consumed by' indicates putting letters inside.
'den' becomes 'nest' (I've seen this before).
'asti' placed inside 'nest' is 'NASTIEST'.
(Other definitions for nastiest that I've seen before include "Most revolting" , "Extremely unpleasant" .)