Rinse some jars with lids in hot water, then drain on a kitchen towel.
Peel, quarter, and dice the quince. Place in a large pot and add enough water to cover the quince by 2 cm (approximately 3/4 of an inch). Bring to a boil, and cook for 40 minutes, or until tender.
Line a strainer with cheesecloth, and set over a bowl. Add the fruit to the strainer, and let drain. Be sure not to press down on the fruit.
Measure the juice, pour into a large pot, and simmer for 5 minutes uncovered. Skim any foam that rises to the top.
The quantity of sugar charge: 250 g of sugar per 250 ml of juice.
Add 250 g (approximately 9 ounces) of sugar per 250 ml (approximately 8 ounces) of juice.
Slowly add the sugar to the juice, and stir until dissolved. Cook until the mixture begins to thicken and set.
Add the drained fruit to the jars, then ladle in the hot jelly. Fill the jars to the brim, wipe the edges, and seal tightly. Turn upside down to cool for 5 minutes. Turn right side up and cool completely.