I have no idea either but I found this on the internet Marina.
Determining Ripeness
Color provides the best guide for determining ripeness. A fully ripe quince turns completely yellow at maturity. The fruit also develops a strong sweet fragrance once it's fully ripe. The fruit also easily snaps off the tree once mature, so if the fruit begin to fall on their own, they are ripe and possibly approaching over-ripeness. Although quinces can continue to ripen after they are picked, they develop the best flavor when allowed to fully mature on the tree.
Harvest
Mature quince fruits snap easily from the tree. If you have to tug on the fruit to remove it from the tree, it isn't quite ripe. To harvest, lift the fruit slightly and twist gently until the stem snaps free. If you must harvest before full maturity, such as before a major frost, cut the stems to remove the fruit so you don't damage the tree or the quince.
Storage
Although a ripe quince may still feel hard at harvest, the fruits begin to soften during storage and they can bruise easily. Store quince in a single layer in a shallow container and avoid placing any weight on them that could damage the fruits. Store the fruits in a cool, dark place, such as in an unheated basement or cool pantry, for up to a month. Inspect the fruits regularly and use or discard any that develop bruises, wrinkling or other signs of damage.
