What boozer craves more than old bottles (7)
I believe the answer is:
ethanol
'what boozer craves' is the definition.
(ethanol is alcohol)
'more than old bottles' is the wordplay.
'bottles' indicates the answer is hidden within the clue (bottling is a kind of containing).
'ETHANOL' is hidden within 'more than old'.
(Other definitions for ethanol that I've seen before include "volatile flammable substance" , "Ethyl alcohol" , "Form of alcohol" , "Intoxicant in wine, spirits, etc" , "Alcohol in wine, beer" .)