The German introduces beer merchant (6)
I believe the answer is:
dealer
'merchant' is the definition.
(I know that merchant can be written as dealer)
'the german introduces beer' is the wordplay.
'the german' becomes 'der' ('the' in German).
'introduces' means one lot of letters goes inside another.
'beer' becomes 'ale' (type of beer).
'der' enclosing 'ale' is 'DEALER'.
(Other definitions for dealer that I've seen before include "The one who distributes the cards" , "Trader as on Stock Exchange" , "Stockjobber" , "One who trades, perhaps on stock exchange" , "See 24" .)