Open mouth consuming first of ripened fruit (5)
I believe the answer is:
grape
'fruit' is the definition.
(grape is a kind of fruit)
'open mouth consuming first of ripened' is the wordplay.
'open mouth' becomes 'gape' (I can't explain this - if you can you should believe this answer much more).
'consuming' indicates putting letters inside.
'first of ripened' becomes 'r' (gst letter of 'ripened').
'gape' enclosing 'r' is 'GRAPE'.
Can you help me to learn more?
(Other definitions for grape that I've seen before include "Green/black fruit" , "In Elgin rummage about in the dark" , "Vineyard fruit" , "Wine fruit" , "Vine berry" .)