Wash the soybeans thoroughly and soak them in water for at least 8 hours.
Drain the soaked beans and rinse them again.
Put the beans and water into a blender and grind until smooth.
Pour the blended mixture into a cheesecloth and squeeze out the liquid.
Pour the extracted soybean liquid into a pot and simmer over low heat, stirring constantly.
When it starts to boil, turn off the heat and let it cool.
Add sugar or salt to taste, if desired.