Just about everyone in the world who’s ever eaten at a Japanese restaurant is familiar with miso-shiru, the soybean-based soup synonymous with Japanese food. Likewise, most people can probably surmise what one of the main ingredients is given that it’s in the name, but maybe not so many are aware that the dashi (broth) component of the soup is actually made from kombu, an edible kelp that is indispensable in imparting the former’s distinctive flavor. It usually comes in dried or powdered form, which is soaked in cold water and heated to near-boiling, and the resulting broth is then used for other purposes.
Kombu is extremely healthy, being chock-full of glutamic acid (a key amino acid for producing umami), iodine, dietary fiber, and potassium, the latter of which helps eliminate the sodium also found in it.
How to Buy It
About 95 percent of all kombu in Japan is cultivated in Hokkaido; however, depending upon the location, there is quite a difference in taste and texture between varieties, the five major ones of which are:
■Ma-kombu (yamadashi kombu) 真昆布（山出し昆布）
Very popular in Osaka, ma-kombu (“true kelp”) is best suited for osuimono (clear fish broth) as it does not tend to cloud the broth. Also well-known for being used in oboro-kombu (dried shredded kelp).
Has a clean taste and is slightly salty with less sweetness than ma-kombu. Very aromatic and hard when dried, it is often used for stock in meals served during the tea ceremony in Kyoto. Also used in ocha-zuke (green tea poured over rice). and senmai-zuke (pickled turnip).
Has a rich flavor and pleasant mouthfeel owing to its suppleness. Often used in su-kombu (pickled kelp) or eaten as is after being thinly sliced. Interesting tidbit: it’s estimated that roughly 70 percent of all the kombu consumed in Toyama Prefecture is rausu-kombu.
Rausu-kombu, often used in su-kombu (pickled seaweed)
■Hidaka-kombu (mitsuishi-kombu) 日高昆布（三石昆布）
This variety is used more often used as a direct ingredient in Japanese dishes such as kombu-maki (kelp-wrapped rolls containing pork or fish) than for stock as it is soft and boils easily. Almost never used in the Kansai region, it is popular in areas north of Kanto.
Hidaka kombu, used in kombu-maki and popular in the Kanto region
Thinner than most other varieties, it keeps its shape after cooking and is often used in oden (Japanese hodge-podge) and tsukudani ( seafood simmered in soy sauce or mirin). Well-known for its use in Okinawan cuisine. Not very well suited for making broth.
So, how do you tell the difference between good and bad kombu? According to Katsuyoshi Suita of kombu specialty shop Suita Shoten in Tsukiji, “it’s quite difficult to distinguish by just looking at it, despite what some people say about dark, thick kombu being better. The same thing is true of natural versus farm-grown kombu. That’s why it’s best to ask an expert at a specialty store and get their advice based on your intended use and budget.”
Mr. Katsuyoshi Suita, owner of Suita Shoten
When to Buy It
Available and in season year-round. Also, it is quite durable and can be stored at room temperature for long periods of time, but preferably in a dark place and not in the refrigerator, where other foods can transfer odors to it.
Suita Shoten, a storied purveyor of all things kombu
Where to Buy It
Kombu is sold in almost every supermarket throughout Japan under a variety of brands and producers, although some brands may be hard to find outside of their respective local areas of production.
In Tokyo, stop by Suita Shoten in Tsukiji for the widest selections available and professional advice.
4-11-1 Tsukiji, Chuo-ku, Tokyo
Open: 6am – 2pm
Closed: Sun/national holidays/market closure day
How to Use It [RECIPE]
While there are several methods for making dashi, one of the easiest ways as recommended by Suita-san is to put the kombu inside a glass jar with water (1.5-2 percent weight relative to the amount of water) and let it sit in the refrigerator for half a day, where it will keep for up to 5 days. If you’re in a hurry, you can steep it in hot water (80 -90 degrees C/176 – 194 degrees F, or just below boiling) for 10 minutes. Use it to make miso soup or kombucha tea.