Pick your fruits and brush them to get rid of the furry stuff on the fruits.
Cut off spoiled black parts and stems. Cut fruits into large chunks and collect in a bowl.
Place quince chunks into a large jam pot and cover with water.
Bring to a boil and cover your pot to cook your fruits through. The quince need to be soft cooked so that the fruits infuse the water.
Take fruits through a fine sieve or cheesecloth. Press fruits to extract juice. Collect quince juice in a large container.
Take the extracted quince juice back to the heat to the cleaned pot and add sugar.
Heat up and bring to a rolling boil.
Reduce heat and keep over a medium to slow heat setting. Cook down your jelly until it's set, this can take about 40-60 minutes.
Skim off foam all the time during the cooking process. That way your jelly will remain clear.
Test if jelly is set with the help of a thermometer and with an ice-cold plate. Drop hot jelly on an ice-cold plate and move around the plate to see if it's running. If it doesn't run it's set. Candy thermometer setting temperature is 220° Fahrenheit/ 105° Celsius.
Pour set jelly into clean sterilized jars up to the rim.
Pour some rum, whiskey or similliar into clean sterilized lids to kill remaining bacteria and close jars with the lids. Turn jars upside down to create a vacuum. Turn jars back when you can touch the hot jars again.
Store jelly jars in a dry and cool environment, away from direct sunlight. (see storing instructions in post).
Video
Notes
Use regular sugar, not pectin sugar.
The ratio should be 1:1 quince juice and sugar. So if your quince juice turns out to be less than 1.3 quart/liter, adjust the sugar weight to the same weight measurement. example 1 quart/liter quince juice = 2.2 pounds/1 kg sugar