The Cast Iron Kettle: called a “Tetsubin” in Japanese, has been produced in Japan for hundreds of years. Here is a great video that can help you understand. It is traditionally a hand crafted object that was developed as an utensil for use in the Japanese Tea Ceremony. These Cast Iron Kettles are made by pouring molten iron into either clay or sand molds. Clay molds are used in the production of high-end artisanal Tetsubin products.
The function of the Tetsubin is unique. It significantly changes the taste of water. When brewing tea using water boiled in Tetsubin, the taste of the tea becomes very mellow and sweet. In addition, thanks to the iron content of the kettle, the resultant water gives us additional health benefits.