Every single quince I ever try to eat, without a fault, has parts on it that have an awful onion-like flavour and leave a disagreeable oniony aftertaste. Most of the fruit is completely free of that flavour, and I have never felt even a hint of it in any quince-flavoured food, like lollipops or juices.
Unfortunately, I can't quite figure out where that awful flavour is contained, and several hypotheses I tried (dark patches of the skin? flesh near the bottom? skin on the bottom? everything touching the hairy part at the bottom?) proved fruitless.
Is there a reliable way to tell which parts of quince will have that awful oniony taste?