Soak the soybeans thoroughly.
Boil the soaked soybeans in boiling water.
Rinse the boiled soybeans in cold water, then peel off the skins.
Put the peeled soybeans in a blender with cold water and blend until smooth.
Strain the blended soybean liquid through a sieve for a smooth texture.
Season with salt or sugar to taste.
Refrigerate and serve chilled.