1.5 - 2 ounces sugar or more, (preferably rock sugar) according to your taste
Fill water in container, add green beans, and wash by rubbing beans with palms of hand. Discard water. Repeat two or three times until water is clear.
Drain green beans, put in pot and fill with 4 cups of water. Cook on medium high heat with lid on until it boils.
Turn heat to medium and let it cook about 20 minutes. You will see that the beans start to plump and split. At this time keep lid partially open, as the boiling water will produce foam which will spill over the pot.
When all the beans have opened and you see the yellow part, time to add sugar. If you do not have rock sugar, use brown sugar. (White sugar gives the soup a sour taste)