Chemically speaking, bletting brings about an increase in sugars and a decrease in acids and tannins (tannins cause the unripe fruit to be puckery). In some cases bletting is simply a ripening process (the fruit is exposed to light frost for a few days after it is ripe), but in others there is a chemical process (water, alcohol or carbon dioxide treatments) used commercially to remove the astringency.
Once the process is complete, the flesh will have broken down enough that it can be spooned out of the skin. The taste of the sticky, mushy substance has been compared to sweet dates and dry applesauce, with a hint of cinnamon. In Notes on a Cellar-Book, the great English oenophile George Saintsbury called bletted medlars the "ideal fruit to accompany wine."
In Shakespeare's Measure for Measure, he alluded to bletting when he wrote (IV. iii. 167) "They would haue married me to the rotten Medler." Thomas Dekker also draws a saucy comparison in his play The Honest Whore: "I scarce know her, for the beauty of her cheek hath, like the moon, suffered strange eclipses since I beheld it: women are like medlars- no sooner ripe but rotten." Elsewhere in literature, D. H. Lawrence dubbed medlars "wineskins of brown morbidity."
There is also an old saying, used in Don Quixote, that "time and straw make the medlars ripe," referring to the bletting process.