The pawpaw plant (Asimina triloba) is a member of the custard apple family and is related to cherimoyas and sweet-sops. It is native to the Eastern United States and commonly grows in a large region from Florida to Canada to Nebraska. Its sweet fruit was eaten by Native Americans and was mentioned in the journal of Lewis and Clark. Today most people are unfamiliar with pawpaws and the fruit can be extremely difficult to find. However, there are certain regions where pawpaws are still popular. Ohio has an annual pawpaw festival during September in the town of Albany.
Pawpaw plants range in size from small shrubs to trees that are thirty feet tall. They grow well in hardwood forest areas and in river-bottom areas with rich soil. The plants produce reddish-purple flowers during June, which develop into single or clusters of papaw fruits in the fall. The fruit looks like a fat banana several inches long. It has a thick green skin that turns brown to black after the first heavy frost, indicating the fruit is fully ripe. The flesh inside the skin is pale and soft like a banana with a pleasant sweet flavor. Inside the flesh are numerous black seeds the size of lima beans.
Those readers looking for pawpaw fruits are most likely out of luck unless they live in the plant’s region. If you are in the Eastern United States, look for pawpaws in supermarkets and farmer's markets between August and October. Choose fruits that are yellow, fragrant, and slightly soft to the touch. Black pawpaws are fully ripe and very sweet but extremely perishable. You can ripen the fruit by leaving it out at room temperature for a couple of days, however the ripe fruit will give off an extremely sweet odor some may find offensive. The ripe fruit is good for only a couple days, but you can extend this time by sticking the fruit in the fridge.
Pawpaws are best eaten raw using a spoon to dig out all the flesh. The only obstacles are the large seeds, which can be eaten but are best spit out. The flesh has a flavor similar to a banana with a hint of tropical fruits like mango and papaya. Pawpaws can also be used like bananas in a myriad of baked goods like breads and muffins. The fruits can also be dried to make chips and they freeze well for longer storage. If you can't find pawpaws, bananas are the best substitute, although you'll miss out on the subtle pawpaw flavors.
The term “pawpaw” is also used to describe the papaya, a completely different species.
The Joy of Cooking, revised edition, 1997
http://www.botany.com/asimina.html
http://www.dispatch.com/news/food/food00/food0920/