Use a rich kind of Merlot ultimately — when bread is served? (9)
I believe the answer is:
eucharist
'when bread is served?' is the definition.
(serving of bread and wine in church)
'use a rich kind of merlot ultimately' is the wordplay.
'kind of' is an anagram indicator.
'ultimately' suggests the final letters.
The final letter of 'merlot' is 't'.
'use'+'a'+'rich'='usearich'
'usearich' anagrammed gives 'eucharis'.
'eucharis'+'t'='EUCHARIST'
(Other definitions for eucharist that I've seen before include "Consecrated bread" , "Mass" , "Bread and wine" , "church service" , "host" .)