According to the "Engishiki" (an ancient book for codes and procedures on national rites and prayers), shiroki was sake brewed from rice harvested from shinden (fields affiliated with a shrine) and filtered as it was, while kuroki was darkened by adding the ash of burned grass roots to shiroki.
『延喜式』によれば、白酒は神田で採れた米で醸造した酒をそのまま濾したもの、黒酒は白酒に草の根の焼灰を加えて黒く着色した酒であると記載されている。