傘が開き、ヒダ立ちが美しいものを香信（こうしん）といいます。
椎茸の傘が７分〜８分程度まで開いたもので、薄手のため戻す時間が短く、スライスやみじん切りにしてちらし寿司やスープ、そうめんの具やつゆなど幅広い料理に使われます。
乾しいたけの旨み成分（グアニル酸）の素となる成分はヒダから出るため、香信は出汁が出やすいと言われています。
An umbrella that opens and has beautiful folds is called koshin.Shiitake mushrooms are about 70% to 80% open, and because they are thin, they take less time to reconstitute, and can be sliced or chopped and used in a wide range of dishes, such as chirashi sushi, soups, somen noodles, and soups.
It is said that the umami component (guanylic acid) of dried shiitake mushrooms comes out from the folds, so it is said that koshin mushrooms can produce soup stock easily.
