Sorbus domestica - True Service Tree

http://en.wikipedia.org/wiki/Sorbus_domestica

http://www.pfaf.org/database/plants.php?Sorbus+domestica

http://worcestershire.whub.org.uk/home/wcc-bio-s19-trueservice-2.pdf

http://www.pfaf.org/leaflets/ady_fruit.php
extract from PFAF article 'Fruit - Food of the Gods':
The bletted fruits. Certain fruits, such as Mespilus germanica (the medlar) and Sorbus domestica, (the service tree) do not ripen fully in this climate. They are picked in late autumn and will then ripen slowly in store. They do not become edible raw until they are almost at the point of going rotten (a process known as bletting), but when at this stage taste like a delicious tropical fruit. However, you do need to be careful because if you overdo the bletting the fruits will ferment in your stomach and cause digestive problems.

http://wbrc.org.uk/WORCRECD/Issue%2015/sorb_tree.htm