I'm not familiar with Manchurian pears per se, but it's also possible you don't have the ID correct anyway, right? What I do know is that pears in general that grow from seed -- which is always a possibility with unfamiliar pear trees -- tend to have a lot of unusual characteristics that make them diverge from the nice "eating pears" that we buy at the grocery store. But often they make good cider, or can be used for cooking, or are good once dehydrated, or make good fodder for animals, or something. One thing that often happens with pears is that after picking there's a bletting process where they undergo fairly substantial changes in texture and flavor right before they turn brown and rot; it's not a decay process quite but it's what makes a Bartlett pear so soft and sweet, for example. So until you've watched these pears sit in a warm place and cut one open every day until they turn into brown moosh, you may not have sampled their full potential. I recommend doing some Google searches on bletting; it's complicated and I don't understand it well enough to explain it fully but it's important when evaluating potentially feral pears.
A simpler question -- when you say "tart" -- are you sure you are describing an acid situation? Or are you describing tannins that make your mouth pucker? Because both are possible, and the distinction matters when it comes to how useful the fruit is. Also, tannins are often concentrated in the skins -- which can often be slipped fairly easily when the fruit is very ripe. Finally, tannins sometimes mellow or go away when the fruit blets or finishes ripening on the tree -- an extreme example of this is with the American Persimmon, but I've seen it happen with feral pears as well.
I hope there's something helpful in this rambling.
Dan Boone wrote:Also, tannins are often concentrated in the skins -- which can often be slipped fairly easily when the fruit is very ripe. Finally, tannins sometimes mellow or go away when the fruit blets or finishes ripening on the tree
My favorite pear tree did this. The tannins were extremely puckery until the fruit was fully ripe. Then they disappeared. Nice thing about it, is that the insects and birds wouldn't bother it, so I could grow organic blemish free pears.