Japanese Dashi from Scratch: Kombu, Bonito, and the Umami Base

Dashi is the most surprising stock in any major cuisine. It takes 15 minutes start to finish. It contains exactly three ingredients (water, kombu, and katsuobushi). It produces a broth so subtle and clear that beginners often think it has not been seasoned. And yet it is the foundation of nearly every savory dish in Japanese cooking. Miso soup, udon broth, dashimaki tamago, oden, simmered vegetables, hot pot bases. All of them start with dashi, and the quality of the dashi determines the ceiling of the finished dish.

The chemistry behind dashi was the original test case for umami. Kikunae Ikeda, the chemist who identified glutamate as a distinct taste in 1908, was studying kombu dashi when he isolated the compound. The reason dashi tastes so concentrated and savory despite its mild appearance is that it is one of the highest natural glutamate concentrations in any cuisine, multiplied by the synergy with bonito’s inosinate.

What kombu brings

Kombu is dried kelp, harvested from cold northern waters, mostly around Hokkaido. The drying concentrates the natural glutamic acid (the source of umami) in the seaweed to extraordinary levels. A piece of good Hidaka kombu contains roughly 2,200 mg of glutamate per 100 grams. Parmesan, by comparison, contains about 1,200 mg per 100 grams. Kombu is one of the highest natural umami sources known.

The glutamate is released into the water by simple soaking. Hot water extracts it faster but also pulls out alginic acid (which makes the broth viscous and slightly fishy) and other less desirable compounds. The classic method uses cold water steeping or very gentle warming, never aggressive boiling. The kombu must be removed before the water reaches a hard boil.

Kombu types vary by region. Hidaka is the most common all-purpose choice. Rishiri produces a slightly richer broth used in many fine restaurants. Ma-kombu is sweeter and used in lighter dishes. Rausu is bolder and used in pot dishes. For a home cook starting out, Hidaka or Rishiri are the easy choices.

What katsuobushi brings

Katsuobushi is skipjack tuna that has been simmered, smoked, dried, fermented with a mold (Aspergillus glaucus), and aged until the block is rock-hard and resonant when tapped. The block is then shaved with a special plane into thin pink-amber flakes. The shaving exposes maximum surface area for fast flavor extraction.

The shaved flakes contain inosinic acid (also called inosinate), which is the second umami compound that pairs with kombu’s glutamate. The synergy between glutamate and inosinate is significant. The two together produce more umami sensation than the sum of either alone. Research shows the synergistic effect can multiply the umami signal by 7 to 8 times compared to glutamate alone at the same total concentration.

The flakes also contribute smoke notes from the smoking process and a faint fish flavor that defines dashi’s character. Hanakatsuo (thin shavings) is the standard for first dashi. Atsukezuri (thicker shavings) is used for stronger second dashi or for niban dashi reuse.

The 15-minute method

The standard recipe for one liter of dashi:

10 grams of kombu (one piece roughly 10 cm by 10 cm).

20 grams of katsuobushi (a generous handful of hanakatsuo).

1 liter of cold water.

Wipe the kombu lightly with a damp cloth to remove surface dust. Do not rinse it (rinsing washes off the surface umami). Place it in cold water and let it steep for 30 minutes if you have time. If you do not, put it on low heat and bring slowly to 140 to 160 F over 10 minutes, then remove the kombu just before the water boils.

If the water reaches a hard boil with the kombu still in it, the broth turns slightly slimy and develops an unpleasant marine bitterness. The rule: kombu out before bubbles break the surface.

Bring the kombu broth to a brief boil. Turn off the heat completely. Add the katsuobushi. The flakes will swirl and then sink. Let them steep for 2 to 5 minutes. Strain through a fine mesh sieve lined with cheesecloth or a coffee filter into a clean container. Do not press the bonito flakes to extract more liquid (pressing pushes out bitter compounds that the gentle steep left behind).

The result is ichiban dashi, or first dashi, with a clear amber color and intense aroma. Use within 24 hours for best flavor. Refrigerated, it keeps 2 to 3 days but loses brightness quickly.

First dashi vs second dashi

The same kombu and katsuobushi can be used twice. After making ichiban dashi, save the used kombu and bonito. To make niban dashi (second dashi), simmer the spent ingredients in fresh water for 10 to 15 minutes, then strain.

Niban dashi is fuller-bodied but less refined than ichiban. The flavor is more aggressive, the umami is still strong, but the clean clarity of the first dashi is gone. Niban is used for braising vegetables, marinades, and stronger-flavored dishes where the delicate top notes of first dashi would be lost anyway. It is also commonly used as the broth base for miso soup in everyday Japanese cooking, since the miso paste dominates the final flavor.

A frugal Japanese home kitchen makes both from the same ingredients in sequence, keeping the first dashi for clear soups and elegant applications, and the second for everyday cooking.

Variations: kombu dashi and shiitake-kombu dashi

For vegetarian or vegan cooking, kombu alone produces a perfectly serviceable stock. Use the same ratio (10 grams of kombu per liter of water), steep in cold water for several hours (or refrigerate overnight), then warm to just before the boil. The flavor is gentler than mixed dashi but still distinctly umami-forward.

Adding dried shiitake mushrooms to a kombu dashi produces shiitake-kombu dashi, used widely in Buddhist temple cooking. The shiitake contributes guanylate, a third umami compound that synergizes with glutamate just as inosinate does. A few dried shiitake (say 3 to 5 medium pieces per liter) steeped overnight along with the kombu, then warmed and strained, produces a deep, woodsy, plant-based stock that holds up against miso, soy, and mirin in most applications.

Common dashi mistakes

Boiling the kombu. The single most common mistake. Hard boiling kombu makes the broth slightly slimy and brings out bitter and overly marine flavors. Pull the kombu before bubbles break the surface.

Simmering the bonito. Bonito flakes should never be simmered. The heat must be off before they go in. Continued boiling extracts harsh, fishy notes that overwhelm the delicate clarity of the broth.

Pressing the bonito at the strain. Squeezing extracts bitter compounds and turbidity. Let it drain naturally.

Using old kombu or bonito. Both lose flavor as they sit. Buy in small quantities and store in airtight containers away from heat and light. Vacuum-sealed packages last 6 to 12 months. Once open, use within 1 to 3 months for best results.

Substituting in dashi-flavored seasoning packets for whole ingredients without expecting the difference. Hondashi works, but it is a different product. For a clear soup where dashi is the entire dish, fresh is significantly better.

What to make first

The most rewarding first dish with fresh dashi is a simple clear soup (osumashi). One bowl of warm dashi, a pinch of salt, a small dot of soy sauce, a single piece of tofu, and a few wakame leaves or a small piece of cooked shrimp. The dashi carries the entire dish. There is nowhere for it to hide. If you have made the dashi correctly, the soup will taste deeply savory and complex despite its near-transparency.

Miso soup is the second easiest application. Half a cup of warm dashi, a teaspoon of miso paste whisked through, a few cubes of tofu, scallion. Done in 5 minutes once the dashi is made. See our methodology for our cookware testing protocols.

Worth the 15 minutes

Once you have made dashi a few times, the process becomes automatic. The ingredients keep in the pantry. The total active time is under 5 minutes. The shelf life of the kombu and bonito is long. And the difference between a Japanese dish made with fresh dashi and the same dish made with water or chicken stock is night and day. It is the single highest-leverage technique in Japanese home cooking.

Frequently asked questions