1. In a bowl, dissolve calcium lactate into orange juice. Pour the mixture into small, demi-spherical molds and let sit in the freezer for 1 hour or until the spheres are frozen.
2. In a rectangular, flat-bottomed bowl and using a hand blender, dissolve sodium alginate in water. Let sit for 15 minutes, then warm briefly in a microwave oven.
3. Unmold frozen orange spheres in alginate bath. Let sit for 3 minutes while gently stirring once in a while to prevent the spheres from touching.
4. Fill a medium-sized bowl with water. using a slotted spoon, delicately collect the spheres and briefly rinse them in the water, then remove excess water from each sphere by applying a piece of paper towel on the bottom of the spoon. reserve.
5. To serve, put each orange sphere in a tasting spoon. Add a dash of melon liqueur in each spoon and decorate with orange zest.