Mentsuyu is salty-sweet soup base made from soy sauce, bonito broth, and mirin (sweet cooking rice wine) or sugar, which is said to be good when prepared on the day before eating.
めんつゆは醤油、カツオ出汁、みりんあるいは砂糖などからなる甘辛いもので、食べる前日に作るのがよいとされる。