mellowing vs ripening

mellowing and ripening both are nouns.

Word	Noun	Adjective	Verb	Adverb
mellowing	Yes	No	No	No
ripening	Yes	No	No	No

As nouns, ripening is a hypernym of mellowing; that is, ripening is a word with a broader meaning than mellowing:

mellowing: the process of becoming mellow
ripening: acquiring desirable qualities by being left undisturbed for some time

Other hypernyms of mellowing include ageing, aging.

mellowing (noun)	ripening (noun)
the process of becoming mellow	coming to full development; becoming mature
	acquiring desirable qualities by being left undisturbed for some time