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' means one lot of letters goes inside another.
'the mixed' is an anagram indicator.
'a'+'stein'='astein'
'astein' with letters rearranged gives 'staine'.
'bar' with letters rearranged gives 'abr'.
'staine' going into 'abr' is 'ABSTAINER'.
'from' acts as a 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" .)