To many people, Dr Pepper tastes as if it contains prune juice.* For years, various sources (including the manufacturers of Dr Pepper) have said that it does not. But that contradiction provokes a question of why to so many people Dr Pepper tastes as if it does. Yet try searching on-line for the answer. Try searching on-line even for the question. One source after another tells us that it doesn't contain prune juice; none seems to explain why (to so many people) it tastes as if it does. None seems even to wonder.
I don't know the answer. But I do know that one of the flavorings in Dr Pepper is … plum. Yeah, that's the fruit that, if dried, becomes a prune. (In fact, some sellers of prunes label them as
dried plums, because people have negative associations with
prune.) I don't know why the manufacturer doesn't add something such as
but does contain plum flavoring to the declarations that Dr Pepper does not contain prune juice. (Side payments from sellers of dried plums seem an unlikely explanation for the silence.)
But the plum may not actually explain the reported flavor like that of prune juice. There are many flavoring agents in Dr Pepper, including apricot and blackberry, and perhaps some of these would in combination still produce the taste of prune juice even were the plum omitted.
*Of course, sensitivity to various chemicals varies across persons, and some individuals might be familiar with tastes for prune juice and for Dr Pepper such that they didn't think that the latter were as if it contained any of the former.