Wash the kuromame thoroughly.
Soak the kuromame in water for more than 6 hours.
Put the soaked kuromame and water in a pot and bring to a boil.
Once it starts boiling, skim off the foam.
Reduce to low heat and add sugar, soy sauce, and salt. Simmer slowly for more than 3 hours.
Boil down until most of the liquid has evaporated.
Let the finished kuromame cool down and serve in a bowl.