Chaucer, Shakespeare, Cervantes, and Rabelais all wrote about the medlar fruit, which must rot before it is ready to eat.
First, the science. The medlar fruit is small, crabapple-like, and when it is picked it is quite inedible: hard, acidic, and full of tannins that give it an unbearable astringency. Despite this, it has been cultivated for thousands of years, beginning with the Greeks and Romans. It can be quite tasty, if you know the trick of it.
Store a medlar somewhere cool and it will blet. Bletting is like rotting, except instead of simple decomposition the fruit will soften, build up sugars, and lose its hefty supply of acids and tannins. The process is similar to fermentation. And although it looks like the medlar is inedible, once it’s mushy brown it’s ready to eat. Apparently it tastes like a musky cinnamon apple sauce.
Second, the literature. As a fruit that is rotten before it is ripe, it has a long literary association with decay and (charmingly) prostitution. It’s also a great fruit for a double entendre, because it looks like a butt. Shakespeare, the Bard of Avon, the crown jewel in Britain’s literary crown, called it an “open-arse.” Poetry, poetry, sheer poetry.
[Thanks to Tania R. for suggesting this topic.]