When we search for dried black beans, we sort out the ones with cracks or small ones to a certain extent and make them the same size. Of course, there are some with cracked or dented skins, but sometimes we find beans that are too dry from the beginning. This is not good either. That's why we select and purchase high-quality beans to begin with. Since these are dried beans, if they are scratched or hit too hard and the skin around them is strongly stimulated, they will break just like glass, so when we spread the beans out on a tray to sort them, we put something like a cloth underneath. Please do not handle them roughly, but do it carefully. If they break, the starch will melt and come out from the inside, which will cause them to spoil and not last long. Black beans at home are wrinkled as much as possible so starch does not come out from the inside very often, but the ones we cook make are made to have the same hardness for the skin and the flesh, so they are inevitably more likely to break.

The beans are put into a pot, and although the ingredients vary from store to store, we use a little bit of baking soda, pour boiling water over it, seal it, and leave it until morning, then put it on the fire. This continues for several days until the skin and the kernel of the beans become completely the same hardness, and once they have completely softened, they are thoroughly soaked in water and any broken beans are separated out. This is why a single black bean can be expensive, costing hundreds of yen in some cases.

By the way, the bad beans that were rejected at first are left together with the other beans when they are soaked to soften them, and then they are passed through a sieve together with the beans that broke during the soaking process and used as is or combined with potatoes to make tea cloths or as appetizers.