Kurokasu (black sake lees)

Kurokasu (黒粕, literally "black lees") is a type of sake lees (sake kasu) produced during sake brewing in which black or brown spots appear on the surface. These spots are caused mainly by oxidative enzymes produced by koji mold, and when they occur they can affect both the appearance and the flavor. To prevent kurokasu, it is important to choose a koji mold with low browning tendency, and additives such as bisulfite (potassium sulfite) are sometimes used as well. This helps maintain the quality of the sake.