Contents: 1 teaspoon (contains 21g-24g) Depending on the recipe, 1 teaspoon of reduced iron is used to cook 200g of black beans. This reduced iron, purchased on December 9, 2025, has been conveniently packaged in individual portions. Shipping will be via Yu-Packet Post. For multiple purchases, the prices are as follows: 2 for 1050 yen 3 for 1350 yen ■ To make black beans black Reduced iron is a very fine powder of metallic iron obtained by reducing iron oxides. It is used to make black beans blacker. Although rusty nails can be used as a substitute for reduced iron, reduced iron is considered better for achieving a black finish.