He won't drink from a stein poured in the mixed bar (9)
I believe the answer is:
abstainer
'he won't drink' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a stein poured in the mixed bar' is the wordplay.
'poured' indicates an anagram (letters get poured or mixed around).
'in' indicates putting letters inside.
'the mixed' is an anagram indicator.
'a'+'stein'='astein'
'astein' anagrammed gives 'staine'.
'bar' anagrammed gives 'abr'.
'staine' put within 'abr' is 'ABSTAINER'.
'from' is the link.
Can you help me to learn more?
(Other definitions for abstainer that I've seen before include "one on the wagon" , "Rechabite" , "Teetotaller" , "Non-drinker" , "He won't vote" .)