posted by Dave Arnold
Kombu, a variety of giant kelp (seaweed), is a cornerstone of Japanese cooking. Kombu is particularly high in free glutamic acid—the umami maker—but its flavor is otherwise rather delicate, so it is an excellent source of MSG. By the way, glutamic acid + sodium = MSG. (You’ll get much more on MSG and umami in our upcoming post: Umami Nation: MSG the Superspice—the Headache is in Your Head.) This post is about kombu broth.
Several types of Kombu are used in Japanese cooking. For a discussion of kombu, I refer you to this website or this book. We used ma kombu which was harvested—as many good things are—in the cold waters off Hokkaido, Japan’s northernmost main island. Yuji Haraguchi of True World Foods, a premier supplier of fish and Japanese products (we buy our fish for ike-jime from them), brought us the kombu.
Ma kombu. High quality stuff from Hokkaido. Brought to us by True World Foods.
Most traditional books will instruct you to place a piece of kombu in cold water and then heat that water until it just begins to bubble, upon which you immediately remove the kombu. But recent work in Japan has shown that optimal glutamate extraction is actually obtained by steeping kombu in 65° C water for about an hour. Several years ago, when we first heard about temperature regulating kombu stocks, we told a group of Kaseiki chefs that they might want to use an immersion circulator. They looked at us like we had three heads (in fact we had only two). Undaunted, we vowed to thoroughly test kombu stocks in the circulator. Two and a half years later, we finally got around to it.
Setting up the tasting.
Setting Up the Test
The tests: we would make one broth traditionally, and one like the Kaiseki do—by attempting to regulate water temperature to 65° C on a typical stove. After carefully reading the dashi sections of some our favorite books, we settled on 10 grams of kombu per liter of liquid—though intuitively this seemed low to us. For a third test we would circulate the kombu in water at 65° C.
We could think of two possible reasons the circulated broth wouldn’t be as good (or better) than other techniques: 1) if the air churned in by circulation had a negative effect, or 2) if the crappy heat control of the stovetop was actually a benefit; i.e., if temperature fluctuation somehow made the stock better. To control for the air problem we added a test of some kombu circulated in a vacuum bag. It didn’t take long for Nils and I to realize the bag was probably a good idea anyway, because we would get some vacuum-infusion benefits.
Yuji from True World also suggested we try some cold infusion, so we added a 10 gram/liter overnight infusion to our test, a 10 gram/liter overnight vacuum infusion, and a 20 gram/liter overnight vacuum infusion. We never heated these infusions with the kombu in them. As a final test, Yuji suggested we heat the regular overnight infusion in the traditional way (until bubbles start to form), with the kombu in it. We ended up with 8 different kombu broths, and we tasted them blind.
What We Didn’t Test
- We didn’t test a temperature range. We didn’t do 60° versus 65° versus 70° C. Next test.
- We didn’t test the level of free glutamate in the broth. Most literature will tell you this number is important. But we can’t measure free glutamate here, and we thought it much more important to judge the broths on taste alone.
- We didn’t test the interaction of the kombu broths with other umami-producing ingredients like bonito flakes (katsuobushi) or shitake mushrooms. Bonito flakes have inosinic acid, and shitakes have guanylate, both of which act synergistically with the glutamic acid in kombu to create a lot more umami than kombu alone.
- Often a kombu is re-used to make a secondary dashi after the primary broth is made. Some of the extraction methods we used rendered the leftover kombu virtually tasteless, which would make a secondary dashi impossible. So we didn’t test secondary dashis.
The Results
Kombu Tasting Results. We tested three different groups (red, blue, and green), and then pitted the winners of each group against each other to figure out which kombu dashi reigned supreme. The red block tested methods of making kombu dashi at 65° C: directly in a circulator, in a vacuum bag in a circulator, and by trying to maintain 65° C on a stovetop. The blue block tested cold infusion techniques: in a vacuum bag at 20 grams kombu per liter, in a vacuum bag at 10 grams kombu per liter (traditional amount), and 10 grams of kombu in a liter of water without a bag. The green group pitted traditional kombu dashi--10 grams per liter started cold and just brought to the bubble and strained, versus cold infused then heated dashi also at 10g/liter without a vacuum bag.
Vacuum bagged 65° C circulated kombu stock reigned supreme!
The verdict was decisive. Unanimous and unequivocal.
In the future, we will test vacuum bagged 65° C kombu at 15 g/liter and at 20 g/liter, because 20g/liter won the cold infusion category. We should also try cold-vacuum-infused-then-heated broth. We think it would win.
Your tasting panel doing a kombu-dashi skoal: Yuji Haraguchi, our buddy from True World Foods and the guy that brought the kombu; Dave; Christina Wang, director of education here at the FCI, kombu lover; Nils.
This is f’ing AMAZING. Seriously. All this time I’ve just been dumping huge sheets and sheets of kombu into boiling for stock. Please do the bonito flake taste test ASAP.
Wow. I second SinoSoul – take this to its logical conclusion and discover the true ultimate dashi.
On a totally unrelated note – I love your skoal glasses. What are they?
Hi Steve,
The glasses are from Ikea. I’m not sure if they are still available. I’ll get their kooky Swedish name for you tommorow.
They are “Svalka” from Ikea…still available! I just saw them last weekend and had to resist the urge to buy yet another set.
http://www.ikea.com/us/en/catalog/products/60015131
Nils really is disturbingly good at skoaling. But for the empty glass, I’m not sure I can tell a difference between the top and bottom shots.
does it have to be bagged for vacuum cold infusion?
Howdy Wylie,
It was a lot better in the bag than just soaking in a cambro. We haven’t tested hitting it in a vacuum machine in an open bain and then letting it sit or using ziplocs. We also haven’t tested shredding the kombu to give more surface area.
What does this mean for those of us without vacuum bags and immersion circulators — I guess the traditional method would be best?
Hi Pablo, I would go with a 5 hour pre-soak then traditional.
What an interesting experiment. I have worked in the kitchen with Yuji – glad you included him on your team – he is always up for trying something new!
Phenominal post! I can’t wait to read more.
Great post! Just curious if and or how u cleaned the kombu prior to testing.
Howdy Cam_13,
We didn’t clean it at all. There is a whole discussion to be had on this subject. I have to re-do my research on the substances on the outside of the kombu.
Very cool! I am firing up the circulator right now!
hey Dave – you guys are great! Did you do anything to try to equalize the temperature in the bag more quickly than normal? Otherwise, how long do you think it took for the temperature in the bag to reach equilibrium? Do you think it’s necessary to add this time to the total cooking time or do you think it’s negligable?
Hi Kenneth T,
Dunno. We didn’t add any cooking time. Probably takes a couple of minutes at least. Maybe 15?
I am somehow not getting why the vacuum would make a difference. I can see that bagging does, but for the vacuum…..?
If it works like quick pickles the vacuum machine would suck out any air that was trapped in the Kombu. It would suck up fluid when I open the bag but this when I discard the Kombu.
Hi JK,
Sorry, I thought I replied to this yesterday but worpress must have shafted me. Here is what I think happens: You suck a vacuum on the kombu in the bag with water, the air is pulled out. The bag is sealed. As the pressure is brought back to 1 atm the water is injected into the voids in the kombu where the air used to be. This rapidly increases the rate of infusion. It is true that we’d probably get even better infusion if we sucked a second vacuum to boil the water back out of the kombu. Worth a test. The reason we didn’t bother is we either let the bags sit around for several hours or we heated them, which probably negates the advantage of a second vac run.
I was making dashi a few weeks ago and reviewing the various arcane heating and steeping methods and thinking to myself that some controlled experiments would be worthwhile. Then I ran across the mini-kombu primer in the back of the Fat Duck book, and got even more excited. Now this! Both excited and disappointed that you’ve gone and done all the work.
Any ideas where mere mortals might get ma-kombu retail in the US?
Great Post Guys!
Just a quick question, what kind of water did you use in testing the Kombu?
I know soft water is best and I know the reasons why but I was just wondering if there’s an optimal type that extracts the glutamic acid particularly well.
Howdie Piggie Smalls,
We used filtered NY City tap water. The filtering was to get rid of the chlorine, etc, that is sometimes in our tap water. NYC tap water is pretty soft. Andrea Illy once told me that the reason coffee is never great here in NY is that our water is too soft (don’t flame me anyone, we have some good coffee here). As to optimal type, we have not run the tests, although I would like to. We have run some more tests already, including different types of kombu, etc, but I haven’t had time to post.
Thanks a lot Dave!
Can’t wait to see the results of your new tests when you get a sec!
One thing I was wondering is how did you vacuum bag the liquid (my only guess was by freezing the water first.)?
Hi Nathan,
What kind of vac do you have? On chamber machines vac’ing liquids is no prob as long as they are cold. On non-chamber machines it is a nightmare.
I thought you might say that. I own a hacked non-chambered vac. machine. but I have access to a large (5.5’x15″) Vac. Chamber that I can run “experiments” in. Hmm… maybe I can use that…
Wow, great post. This is exactly the type of experiments that beg me to perform them, but then not come around to. I did once get absolutely nuts over pickling trying a different range of vinegars, sugar/vinegar levels and pickling times.
Dave,
So traditional dashi making (no pre-soaking) is absolutely the worst way to go? Interesting. I have a vacuum machine, so I could better vacuum pack 10g of kombu and let it sit instead of soaking and bringing it to a simmer (without gadgets)?
Howdy Auldo,
Our current favorite (not posted yet, soon), is 20 grams/liter vac’ed down and circulated for an hour at 65 C.
Great post! I’d be interested in your results when steeping bonito into the dashi for soup stocks. I’ve been making dashi almost everyday many years. I find the gently heating the water and konmbu for long time (starting with cold water). Once it reaches the simmering point I’ll add bonito flakes and steep for no more than 15 minutes (seems to go down hill after that). Perhaps heating it slowly is a crude way of getting the most time at 65 C. But I really think the bonito imparts the most flavor when stock is quite hot. What do you think?
Awesome blog. Thanks!
Hi Benjamin,
We haven’t done our bonito tests yet. We hope to soon. We want to test length of steep, temperature, and thickness of slice. We also want to test with chiai and without.
Hi Chef,
Any chance you’ve taken a look at dashi with bonito yet? If you haven’t really tested it I’d be interested to know any of your thoughts / current procedure anyway.
I’m living and working in Japan and make dashi every day more or less the traditional way. After reading this post I can’t wait to try it in my home-made circulator. Don’t have a vac machine unfortunately.
Incidentally, I saw you mention Ayu fish sauce in another post. No one I know here had heard of it, but I found some quite easily looking online and ordered it. I love ayu and I love fish sauces, so I’m tremendously excited to try this.
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I know I am probably not the level of cook you normally get here, but I am hoping you could help me understand the process by which you vacuumed the kombu. I mean, pretend I don’t know anything … because I don’t. Does the kombu get ssealed then put in the water? Does 1L water go in with the kombu, get sealed and circulated? Sorry, I know this is pretty rudimentary stuff to you guys but I am looking to make a better dashi than I am currently making. Many thanks for your patience!
Howdy Christopher, Sorry it took so long to get back.
Add ice water to the bag and then the kombu. Then vacuum seal in a chamber vac (you’d have trouble in a home vac), then circulate.
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