Scrupulously scrape quinces with a clean dish towel to remove fine fuzz on fruit. Wash and cut into pieces, removing blossoms and stems, cut flesh into slices.
Put quinces in a saucepan with 1 liter of water and white wine and soften for 30-40 minutes. Cool slightly, then pour into a sieve lined with a muslin cloth and drain the juice. Later, tie the tips of the cloth and hang them up so that the juice drains even better, preferably for one night.
Measure the obtained juice and add the same mass of sugar, let the mixture bubble up and meanwhile boil it down, skimming it again and again. Make hearty until the jelly sample succeeds, that is, a drop placed on a cold saucer solidifies on the spot. This takes about 40-50 min. Fill the finished jelly hot into clean jars and seal on the spot.