Preparing the quince is rather hard work. So, I recommend making no more than about 3 kg of fruit at a time. That should be about 5 kg before peeling.

Wash the quince well. Rub the fine downy fuzz off of the surface.

To prepare the quince: Put the quince and water in a large pot. Bring to a boil and cook the quince until they are tender.

Take the fruit out of the hot water and let them cool down. Peel them and remove the stem ends. Roughly chop up the fruit and place them in another pot or in a storage container.

(You don't have to peel the quince in advance. If you boil the quince until they are falling apart, then the skin and the outer part of the flesh can be removed together.)

When the fruit has been processed, weigh it out. Calculate 40% of that weight and that will be the amount of sugar to use. (You can increase or decrease the amount to taste.)

Mash the fruit using a hand-held blender or similar device. Put the mashed fruit in a pot.

Add the lemon juice and sugar to the pot, and start cooking over low-medium heat. Simmer and reduce slowly while mixing. Be careful not to burn yourself.

You may get burned if the contents of the pot splatter, so don't leave the pot unattended for too long. Stir while simmering and reduce it over low-medium heat.

When the pulp turns orange, remove from heat. Pour the pulp into the prepared tray. Be careful not to burn yourself.

Note: This version doesn't have a lot of sugar, so it won't turn brown like commercially sold quince jelly.

Dry the jelly in a cool location out of direct sunlight. (If you use 40% sugar, this takes 5 days to a week.)

Slice into pieces. Wrap each piece in plastic. Freeze to store for a long period. Refrigerate any pieces you're going to eat it right away.

Note: The top surface should be firm and the bottom surface still soft right after you finish drying. If you wrap the pieces up and store them with the firm side down, the texture will gradually even out.