How to make
Wash the quinces. If you are not sure of their origin, peel them. Grate them on a coarse grater. The amount you need is 1 kg of grated quinces.
Mix the grated fruit with 1 kg of gelling sugar and mix very well. The sugar should be well moistened by the juice of the quinces. Leave them for 10 minutes.
Put the pot with the grated quinces on the stove and turn on the maximum temperature. Stir constantly, until the mixture boils.
Reduce the heat on the stove to medium or low. That way it won't splatter during boiling.
After the quinces have boiled for 10 minutes, remove them from the heat and puree them. Be careful not to burn yourself.
Place them back onto the heat and boil for another 5 minutes. Stir almost continuously, until the marmalade is done. The time I made mine in was 15 minutes.
Once it has thickened enough (test by pouring a small amount into a dry plate), add 1 teaspoon of citric acid and let it boil for a minute or two more, by stirring constantly, so that it doesn't burn.
Pour the hot Portuguese quince marmalade immediately and close the jars.
Turn them upside down and leave them to cool.
