Sin getting into reserved wine (6)
I believe the answer is:
sherry
'wine' is the definition.
(sherry is a kind of wine)
'sin getting into reserved' is the wordplay.
'sin' becomes 'err' (to sin is to err morally).
'getting into' means one lot of letters goes inside another.
'reserved' becomes 'shy' (I've seen this before).
'err' put into 'shy' is 'SHERRY'.
(Other definitions for sherry that I've seen before include "Spanish drink" , "Spanish fortified wine" , "Fortified wine originally from Spain" , "Fortified wine from Jerez" , "Wine from the Jerez region of Spain" .)