Rennet's first to be accepted by man before making cheese (7)
I believe the answer is:
gruyere
'cheese' is the definition.
(Gruyere is an example)
'rennet's first to be accepted by man before' is the wordplay.
'rennet's first' becomes 'r' (gst letter of 'rennet').
'to be accepted by' is an insertion indicator (inserted letters are accepted).
'man' becomes 'guy' (guy is a kind of man).
'before' becomes 'ere' (poetic term for 'before').
'r' inserted within 'guy' is 'gruy'.
'gruy'+'ere'='GRUYERE'
'making' acts as a link.
(Other definitions for gruyere that I've seen before include "Whole-milk holey cheese" , "Firm Swiss cheese" , "Swiss cheese with small holes" , "Firm pale cheese with holes" , "Tangy cheese" .)