Steps

1. Lightly wash the black beans and drain them.
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2. Add 6 times the amount of water as black beans (e.g., 1200ml of water for 200g of black beans) to the pot with the washed black beans.
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3. Let the black beans soak for 9 to 12 hours until plump and wrinkle-free. [This is the key!] It's important to start cooking from a state where the beans are plump and wrinkle-free, as they will be when eaten.
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4. Add sugar equal to the weight of the black beans (e.g., 200g of sugar) to the plumped black beans.
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5. Gently mix to distribute the sugar evenly.
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6. Place the pot with a lid over medium heat and bring to a boil.
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7. Once boiling, carefully skim off any scum that rises to the surface.
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8. After removing the scum, reduce the heat to very low.
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9. Place a drop lid (or paper towel) in the pot, cover with an inner lid, and then a slightly ajar outer lid (propped with chopsticks or similar to allow steam to escape). Simmer on very low heat for 3 to 4 hours. [This is the key!] Beans tend to wrinkle if exposed to air, so it's important to prevent air contact with the inner lid.
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10. After 3 hours, take out one bean and check if it easily crushes with chopsticks, or taste it to confirm tenderness.
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11. Once tender, add 1 tsp of soy sauce, stir to combine, and turn off the heat.
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12. Allow the black beans to cool to room temperature with the drop lid (or paper towel) in place to ensure they remain submerged in the liquid.
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