The main issue is flavour (6)
I believe the answer is:
season
'is flavour' is the definition.
(I've seen this before)
'the main issue' is the wordplay.
'the main' becomes 'sea' ('sea' can be a synonym of 'main').
'issue' becomes 'son' (issue can mean someone's offspring).
'sea'+'son'='SEASON'
(Other definitions for season that I've seen before include "eg.Summer" , "Period of a year" , "Add salt, pepper, spices etc" , "Add condiments to for time of year" , "Salt, maybe" .)