Wash quinces thoroughly and cut them into small pieces (including the core). Put quinces and 3 litres of water in a pot. Cover and simmer for about 1 hour. Put the quinces on two large sieves, each with a moistened gauze cloth and let them drain overnight. Measure out 2700 ml of juice.
Mix juice and jam sugar well in a pot. Bring to the boil at high heat and boil for approx. 4 minutes while stirring continuously. Immediately fill prepared glasses with jelly, close them and put them on the lid. After approx. 5 minutes turn them over again and let them cool down
Waiting time approx. 12 hours