Source of Chardonnay -- a very American drink (4)
I believe the answer is:
cava
'drink' is the definition.
(alcoholic drink)
'source of chardonnay a very american' is the wordplay.
'source of' suggests taking the first letters.
'a very' becomes 'av' (I've seen this in other clues).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
The initial letter of 'chardonnay' is 'c'.
'c'+'av'+'a'='CAVA'
(Other definitions for cava that I've seen before include "Spanish fizz" , "sparkling drink" , "Sparkler" , "Spanish bubbly" , "Spanish "champagne"" .)