Do you know the answer to this simple question? First, sake rice grains are more prominent, so they are not easily cracked when shaving off the minerals that cause bitterness. Also, the center of the grains, called “shinpaku,” needs to be larger and oval. This is where koji mold enters and develops to ferment nicely and produce koji that melts well. The popular Yamada Nishiki, known as the “king of rice,” meets these conditions.