Tasting an apple happens in stages. The first thing you get is the snap, the mouth feel. Then comes sweetness. Giving the flavor complexity is a varying amount of astringency or acidity. Then there's a salt taste.
Aroma is what makes an apple memorable.
It adds depth to the eating experience. It gives the apple character. What gives apples their aroma is the release of volatile molecules, mostly esters, concentrated in the skin and outer flesh. Because most of the apple's color production also occurs in the skin, Fellman and his colleagues became interested in the biochemical relationship between color and aroma. About 335 different compounds have been identified in the apple.