Best stout drunk across heart of Germany (6)
I believe the answer is:
utmost
'best' is the definition.
(to do your best is to do your utmost)
'stout drunk across heart of germany' is the wordplay.
'drunk' indicates an anagram.
'across' indicates putting letters inside.
'heart of' says to take the centre.
The centre of 'germany' is 'm'.
'stout' with letters rearranged gives 'utost'.
'utost' going around 'm' is 'UTMOST'.
(Other definitions for utmost that I've seen before include "At furthest limit" , "Finest" , "(To the) greatest possible extent" , "Maximum effort" , "Furthest or extreme" .)