Cocktail with orange juice and vermouth is swallowed in an instant (6)
I believe the answer is:
mojito
'cocktail' is the definition.
(rum-based cocktail)
'orange juice and vermouth is swallowed in an instant' is the wordplay.
'orange juice' becomes 'oj'.
'and' is a charade indicator (letters next to each other).
'vermouth' becomes 'it' (short for 'Italian vermouth' as in 'gin and it').
'is swallowed in' indicates putting letters inside.
'an instant' becomes 'mo'.
'oj'+'it'='ojit'
'ojit' put inside 'mo' is 'MOJITO'.
'with' acts as a link.
(Other definitions for mojito that I've seen before include "Cuban cocktail with rum as a base" , "Minty cocktail" , "Mexican cocktail made with white rum and lime juice" , "Cuban rum-and-lime-based cocktail" , "'Cuban cocktail made from rum, lime etc (6)'" .)