Iron (tetsu)

Iron is an important element in sake brewing, yet it is also one of the harmful components. If the brewing water contains iron, it can combine with substances produced by koji mold in the moromi (fermentation mash), causing the sake to turn reddish-brown. This discoloration affects the appearance and quality of the finished sake and can degrade its flavor. In addition, because iron is difficult to remove by activated carbon filtration, it is extremely important that brewing water be free of iron. For this reason, care is also required to avoid using iron in the tools and equipment used in sake brewing. These measures make it possible to maintain the quality of clear, clean sake.