Kombu has different characteristics depending on where it was harvested, and different kinds of kombu are used for different purposes.
Rausu (羅臼) kombu, is a brownish kelp that, with its desirable aroma and soft texture, is prized for the rich flavor it imparts to stock and is the top choice for tsukudani.
Hidaka (日高) kombu is dark green to near-black in color and readily takes on a soft texture when boiled. Hidaka konbu is also used for stock and is a favorite for oden and kombumaki (kombu rolls).
Text by Kitchen Nippon