Rinse the black soybeans thoroughly and soak for at least 6 hours.
Boil the soaked black soybeans in boiling water for 10 minutes.
Rinse the boiled soybeans in cold water and let them cool.
Blend the black soybeans with water and salt until smooth.
Strain the blended mixture through a fine mesh strainer or cheesecloth.
Pour the strained soy milk into a pot, bring it to a boil, and finish.