Former ingredient of cool drinks (3)
I believe the answer is:
old
'former' is the definition.
(both can mean previous)
'ingredient of cool drinks' is the wordplay.
'ingredient of' indicates the answer is hidden within the clue.
'OLD' is hidden in the letters of 'cool drinks'.
(Other definitions for old that I've seen before include "Stale" , "Wild clematis" , "Vintage" , "No longer young" , "Venerable" .)