I have a tree that produces loads of beautiful red, cherries. The nursery man we bought it from said the cherries would be sweet and about the size of Bing cherries. They are that size, but they are very sour. They make wonderful jelly but, in order to make a pie that is edible, I have to add about twice the amount of sugar called for. Is there any way to treat the cherries to dimish the sour/bitter taste before making the pie filling?