A brew and 50 per cent blissful is burgundy (7)
I believe the answer is:
chablis
'burgundy' is the definition.
(Chablis is an example)
'a brew and 50 per cent' is the wordplay.
'a brew' becomes 'cha' (I've seen this in other clues).
'and' is a charade indicator (letters next to each other).
'50' suggests halving the letters.
'per' becomes 'by'.
'cent' becomes 'lis' (I can't justify this - if you can you should believe this answer much more).
'by' halved is 'b'.
'cha'+'b'+'lis'='CHABLIS'
'blissful is' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for chablis that I've seen before include "French town noted for white Burgundy wines" , "Dry white Burgundy" , "Dry Burgundy wine" , "Town in north central France noted for white Burgundy wines" , "Drink" .)