Wash organic oranges thoroughly under hot water, rub dry. Peel in fine strips with a zest ripper. Cut all oranges in half and squeeze the juice. Measure out 600 ml juice.
Wash kumquats and carambola and dab dry. Cut the kumquats into slices and remove the seeds. Cut carambola into thin slices.
Put the orange juice, jam sugar, kumquats and orange zest in a wide, high pot. Bring to the boil while stirring, add carambolic slices, cook for about 4 minutes until bubbly. Possibly make a gelling test.
Pour hot jam into jars with twist-off lids, close them immediately and turn them upside down for about 5 minutes. Leave jam to cool overnight, wrap up nicely.