Kombu

Kombu is a kelp used in most Japanese cuisines. It is rarely eaten alone except in Okinawan cuisine, but used to enhance the flavors of fish. The mineral content of the kombu matches well with most seafoods, and can not be ignored when cooking Japanese food.  Kombu is first dried before they are sold.

Kombu is also the main ingredient used to extract monosodium glutamate or MSG. Only small amounts of MSG can be extracted from a piece of kombu, but natural levels of the compound make the food taste the best, and artificially extracted salts should not be used to flavor dishes for it can alter the taste. 

Kombu is always simmered to brew the flavors. It is important to place it in cold water and then heat it to a simmering temperature. Once the water starts simmering, then it is discarded after 30 sec or so. Not much time is needed to brew kombu since it can start to release strong kelp flavors if done too long.