- Rinse kuromame, then drain and set aside.
- In a large pot, add water, soy sauce, salt and sugar and bring to boil. Stir until sugar has dissolved. Turn off the heat and add kuromame to the pot. Make sure the beans well immersed in the liquid and that they are added to hot liquid so that the beans will not wrinkle while cooking later on.
- Cover the pot and leave to soak overnight.
- Next day, bring the pot to boil, then reduce to low heat. White bubbles will appear on the surface. Skim the scum as the beans start cooking. This will help to remove any bitterness.
- Add a round piece of parchment paper to the pot to ensure the beans are submerged. Continue to simmer the beans on low heat for 5-6 hours, or until beans are tender. If liquid level is low, add some water.
- Strain the beans and remove from heat. Continue to boil the syrup until it thickens to a glossy texture and black colour. Pour syrup over beans and refrigerate overnight before serving.