Preparation: Wash the quinces and peel them, then wrap them in a towel that's been soaked in salt water, so they don't darken. Boil a sauce from the sugar and 4 cups of water - remove the foam with a slotted spoon. The sauce needs to be medium thick.
Grate the quinces on a coarse grater directly into the container with the sauce. Boil the quinces until the syrup starts to thicken. Add the citric acid and let the jam boil for 2 more minutes. Once it cools, distribute it into jars and close them.
You can also add raisins, to get an even more flavorful and delicious jam. Add the raisins along with the citric acid. Instead of raisins (or along with them), you can also add finely chopped pieces of walnuts.
If you prefer, you can make a quince jelly. Wash and chop 4.5 lb of quinces into pieces - along with the fruits' cores. Pour 12 1/2 cups of water over them and boil on low heat - the juice needs to turn red, then turn off the heat.
Pour the quinces into a colander and drain out the juice, then strain it, so that there are no seeds or pieces of fruits. Once the juice cools, add 2 lb of sugar to it and return it to the stove - you need to boil it on medium heat until the mixture starts to gel.
Several minutes before removing the almost ready jelly from the stove, add 1/2 cup citric acid. Pour the prepared jelly into an appropriate glass container.