It's by way of being an extract of caviar (3)
I believe the answer is:
via
'it's by way of' is the definition.
(via means by way of or by means of)
'an extract of caviar' is the wordplay.
'an extract of' indicates the answer is hidden within the clue (I've seen this in other clues).
'VIA' can be found hidden inside 'caviar'.
'being' is the link.
(Other definitions for via that I've seen before include "A Roman way" , "Going through" , "Roman road" , "Passing through" , "By means of" .)