But this Morton's Salt ad from 1949 makes it sound like, well, of course this is what people do. It does so much for grapefruit, the 1940s Morton ads all say. Yes, it does. It makes them salty.
A 1946 ad from Morton's says that there are "special displays" of Morton's-plus-grapefruit in all the best grocery stores:. This was probably because the yellow grapefruit looked good with the girl in the yellow dress and yellow umbrella on the blue Morton's box. The 1946 ad copy goes on to rave poetically about cool salt and tingling grapefruit flavor:
Perhaps you've heard about it - wondered about it. Why not try it? This cool, pure salt on grapefruit brings out all the delicate, taste-tingling flavor at its best...You'll discover flavor you never knew.
So did Morton's think this pairing up as a brilliant marketing strategy? Another Morton's ad (from 1947) says that, well, they don't really know whose idea it was - maybe it was the Florida citrus growers. And you know what? I did a little bit of research (not a lot, just a little) and this is exactly right. You see, back in 1917, it was reported in the United Mine Workers Journal that there had been a sugar shortage and this impacted the grapefruit market quite a bit - so much so, that the growers suggested to people that they use salt instead of sugar. And apparently putting salt on all kinds of fruits really does bring out their flavor - see this thread over at Chowhound, for example, to see some examples.