Kombu (aka Kelp) is a Seaweed, that is essential in Japanese cuisine, especially for preparing ‘Dashi’ stocks. Read on to learn how to use it.
It would be almost impossible to have eaten in a Japanese Restaurant and not have encountered Kombu in one form or another. It can be eaten as a vegetable in it’s own right, but it is a foundation ingredient in Japanese cuisine for the preparation of Dashi stocks.
Miso soup, to name one ubiquitous and very popular dish, is based on Dashi, and there are many dishes which just cannot be made without the very interesting, and umami-rich sea vegetable you see pictured in its dried form above.
What is Kombu?
You may, at one time or another, when walking on the shore, have come across a variety of large, ribbon-like seaweed cast up on the shore, possibly with the olive-green fronds still attached to a thick, rope-like stem. For years, I knew the basic type simply as ‘Kelp’ but, point of fact, that name actually includes a whole range of very different seaweeds (many of which are edible) and the sort you see pictured above is more properly referred to by its Japanese name ‘Kombu’ (or, less frequently, ‘Konbu’).
Kombu is not a ‘rock seaweed’ like others you may find growing along the shore, rather it occurs in deeper waters where the long thin fronds, properly known as ‘blades’ are attached to the bottom by the ropy stems known as the ‘stipes’. It is extremely fast growing, with blades reaching up to 80 meters long, and often occurs in dense ‘forests’ as shown above. I can only imagine that swimming through these in scuba gear must be a very eerie experience indeed.
What does Kombu Taste like?
Well, Kombu is, of course, a seaweed, and, to put it simply, it tastes like a seaweed. For many Westerners who have not actually put a piece of seaweed into their mouth and tasted it, the idea can be a bit daunting. In fact, though, most people find they like it.
Dried Kombu, as shown in the very first picture, can be eaten as is. The texture is crisp, and slightly crunchy, and the taste, as well as the aroma, are very much the essence of the sea. Kelp, or Kombu, in one sense tastes like the smell of the shoreline, with a faintly salty marine quality with a definite umami base.
Once soaked and reconstituted, the basic flavor remains and the texture changes to something with a chewy bite, and a slightly slippery, gelatinous mouthfeel. It is, I would say, somewhere between thin pasta that is not quite al dente, and a very thick Apple skin.
Purchasing and Using Kombu
You most commonly find Kombu packaged in whole blade sections cut to anywhere from 6 to 12 inches long, as shown in the very first picture.. You can, however, find dried Kombu that is cut in squares, strips, or slivers, and a granular form can also be found which used alone, or with other ingredients such as ground dried fish, to make a Furikake, which can be sprinkled over rice, or used to flavor other preparations.
The dried blade can be eaten as is, if you like, but it is also sold in small bite size pieces to be used as a snack (perhaps alongside sake or a beer). Typically, however, it is reconstituted by soaking for use in other preparations.
Here you can see a section of dried blade in close-up. You should note the whitish residue adhering to the surface as this is an important feature. Some of it is straight sea salt, whilst some is composed of naturally occurring glutamates, including monosodium glutamate, and these pack a lot of flavor. Accordingly, you should never wash or rinse kombu as you will only be flushing away some of the best taste. If you are very fastidious, you can, as some suggest, wipe the surface with a damp cloth but, personally, I don’t bother with this (and have thus far lived to tell the tale).
Reconstituting Kombu by soaking
To reconstitute kombu, all you need do is to soak it in warm water. Here you can see the piece from the previous picture that was soaked for about 15 minutes in 4 cups of water. The small section has now almost tripled in size and is very soft and pliable. It can now be sliced and eaten immediately in cold preparations or else added to other ingredients to be cooked.
Pieces of the whole blade are also reconstituted and added to soup, stews or simmered dishes, as well as to rice or noodles but, in the main, the primary use of Kombu, at least in Japanese cuisine, is as a source of umami essence. One good example of this is in the preparation of Sushi rice, wherein a strip of Kombu is added to the rice water as it is cooking (and later removed).
Beyond the snack usage mentioned above, Kombu, once soaked, is often used in Chinese, Japanese and Korean cuisine as a salad ingredient. The Japanese take this even further and pickle it in rice vinegar, and both the Japanese and Koreans prepare it with soy, sugar and other ingredients to make cold dishes that keep well and can be used as condiments or banchan.
The above picture shows strips of reconstituted Kombu used in a cooked dish. This dish is a type of Japanese Relish known as Kombu Tsukudani, which is typically served as one of several ‘Small Plate’ dishes as part of a Japanese meal, much as ‘Banchan’ are used at the Korean table.
Now, all the other uses aside, the real importance of Kombu is in the preparation of broth or stocks, particularly the quintessential Japanese stock known as Dashi. Since this preparation forms the base of so many other dishes, it is difficult to imagine a Japanese meal that does not include the use of Kombu somewhere in the menu.
Typically, when one speaks of Dashi without qualifying it further, one refers to a stock made from both Kombu and a fish component. Typically, the fish essence is derived from shavings of dried, smoked bonito known as Katsuobushi, but smaller dried fish such as anchovy or sardine are also used.
However, just as a dashi could be made purely from fish, or even dried mushrooms, so can a light, vegetarian preparation, known as Kombu Dashi, be made from just Kombu alone…
How do you make Kombu Dashi?
There are two methods of making Kombu Dashi, one with cold water and one with hot. The cold-water type takes longer to make, but has the advantage of requiring no oversight. The hot-water sort, however, is very quick to prepare but you have to take some extra care.
The ratio of water to Kombu is the same for both methods. Basically, the ratio is 4 cups of water for a piece of dried Kombu measuring approximately 8 inches by 5 inches (or 20cm by 12cm, more or less). If you have smaller pieces, or broken pieces adding up to a slightly different surface area, just adjust the water ratio accordingly.
For cold water dashi, just cover the kombu with the appropriate amount of water and then set aside to soak for 12 hours or so. If you like, you can just stick it in the fridge overnight and have the dashi ready for use the next day.
Here, as shown in the above picture, I have set the Kombu in cold water and placed it in the sun. In point of fact, I only did this to allow the Kombu to soften enough to be submerged, and to take the picture. After that, the jar went into the fridge to steep overnight.
Here you can see that the resultant stock is a nice light color. The picture, unfortunately shows the Kombu Dashi as being slightly opaque, but in fact, it is quite clear and rather resembles a White Wine. Depending on your Kombu, the tint can vary from slightly greenish, to a more golden color.
The taste is very subtle but beautifully flavored with a nice umami body that just barely betrays its marine origins. The vague meaty taste could easily be mistaken for a delicately seasoned, but very light chicken broth in some ways and, if you didn’t know what you were tasting, you would be hard-pressed to identify the source as seaweed at all.
The second, and more common method of making Kombu Dashi, is to soak the dried seaweed for 30 minutes or so in a suitable pot and then bring it to just below the boiling point over low heat. As soon as this happens, remove the pot from the heat and let it steep for a few minutes longer.
Allowing the liquid to boil will change the character of the resultant stock. Some say it introduces unpleasant fishy tastes and, while I don’t find this myself, the taste is certainly altered. For the proper flavor, for Japanese dishes, it is very important that the stock reach no more than a gentle simmer and the Kombu removed after just a few minutes.
Here is a pot of Kombu Dashi prepared by simmering after the Kombu has been removed. The color here is a bit more golden but you can definitely see the clarity.
Finally, don’t throw away the Kombu after it has done its initial job. At this stage, it can still be used in other dishes or, if you like, you can do a ‘second run’ with a fresh batch of water. In Japanese culinary terms, the first use of Kombu (and other ingredients) produces an ‘Ichiban Dashi’, or ‘number one stock’, while a second run is called ‘Niban Dashi’ or ‘number two stock’.
To make a Niban Kombu Dashi, add the Kombu used in either a cold or hot water Ichiban Dashi and simmer it for about 15 minutes in another 4 cups of water. Generally, the result would not be used for soups, but this second run still has good flavor and is certainly suitable for richer preparations such as stews or simmered dishes.
To try out a fresh batch of Kombu Dashi, try stirring in a little Miso, some green onion, and maybe a few clams or some such, for a delicious soup.
The above picture shows a preparation called Kakejiru which has multiple uses, but is especially favored as a noodle broth. Typically, this is made with a full Dashi composed of both Kombu and Katsuobushi, but for Vegan or Vegetarian dishes, you can also make it with just a plain Kombu Dashi.
I had never heard of the cold water method to make dashi before. I have used sous vide to do the extraction slowly (couple of hours) at 60C/140F. In Japan I’ve also had the pleasure of trying fresh kombu. It was served with a small pot of boiling water, in which you were supposed to blanch the kombu briefly before eating. The color turned instantly from olive green to a very bright green. It was very crunchy and served with rice vinegar to dip in.
I have really only made the cold water variety out of interest. It is more practical to use hot water. We sometimes see Kelp washed up on the beaches around here. I have never tried harvesting it myself, but I wouldn’t mind trying it as you had it in Japan.