Gentle Washing

Dried kombu used to be washed or wiped to get rid of dirt and impurity but nowadays most kombu is clean enough to be used straightaway. If the kombu does require cleaning, it should never be washed vigorously, as this will result in the loss of important salt and other substances contained on its surface. The sodium content in fresh kombu is not very strong, but when dried so that the water content is reduced to around 7-10%, a high proportion of the salt and mannite (a polyol, or sugar alcohol) contained within the seaweed emerge onto its surface. Thus, a thorough washing of the kombu surface will result in a substantial loss of these substances. However, a quick rinsing will cause no great loss, whilst still being effective in removing dust and dirt. If you are wiping the kombu, make sure to use a cloth that has been wrung out well, and wipe gently.