Chef’s first to forsake moreish ingredient (8)
I believe the answer is:
'ingredient' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for additive that I've seen before include "Something joined, to food say", "flavouring perhaps", "Produced by summing", "Supplement", "Flavour enhancer".)