Wash untreated oranges. Peel thinly and cut into fine strips. Peel ginger and cut into fine strips as well. Squeeze all oranges. Wash the lemon balm leaves and cut into strips.
Measure out 1 litre of orange juice. Pour into a pot through a sieve lined with kitchen paper. Add orange peel, ginger and jam sugar, stir and bring to the boil. Cook for 1 minute until bubbly.
Add lemon balm and liqueur. Pour immediately into prepared glasses and close tightly.