Use less sugar or no sugar if you like the basic sweetness of the fruit. The orange also adds sugar and orange zest gives the marmalade a pronounced zesty acidity while the pulp adds a tinge of bitterness.
Our lemon kumquats are sour and so we wait till they fall of the tree to eat them. The tree is planted in a pot outside the front door for full southern exposure.
One small apple peeled and cored diced fine (used for its pectin and as a sugar substitute.)
Twelve to 20 kumquats chopped into small piecies. For the larger kumquats cut them in three, then remove the seeds and then chop. Should make two cups.
One orange, zest peeled with a potato peeler, then zest chopped fine, then pith removed and tossed, and then the fruit cut fine.
Mix and cook in the 5” pot for two hours in the summer position to get the fruit soft and mushy.
Stir two cups organic brown fair trade sugar into lemon mixture and let cool for a couple of hours. Organic brown fair trade sugar is sold at Whole Foods and other stores under the name Organic Sucanat. Look for the Fair Trade certified label. As you can tell from the recipes we use very little sugar so we might as well buy the kind that will do right by the people and the planet.
Using a slotted spoon transfer most of the fruit to a blender and puree. Return to the pot, in the summer position, for another hour. The sun is almost 30 deg east from the winter rise and much higher in the sky making the summer position possible from 10:00 AM to 3:00 PM.
Let cool, bottle and save in the refrigerator. I use standard, recycled bottles, because the sugar is a preservative. If you are going to give it away as gifts learn how to use and process canning jars. and check the wiki.