Kombu (also called kelp) is a type of sun-dried seaweed that has been processed into sheets. It should not be rinsed with water before using or it will lose some of its flavor; instead, lightly wipe it with a dry cloth. Unopened packages will keep indefinitely; after opening, store kombu in a resealable plastic bag in a cool, dry place and use within 6 months.
Bonito flakes are made by boiling, smoking, sun-Âdrying, and then flaking fresh bonito, a type of small tuna. Store in an airtight container in a cool, dry spot for as long as a year (check the label for a freshness date).