What Is Dashi and Why Does It Matter?

If Japanese cooking had a single secret, it would be dashi (出汁). Awase dashi (合わせ出汁), the most popular and versatile variety, is a simple stock made from just two ingredients: kombu (dried kelp) and katsuobushi (dried bonito flakes). It is the quiet foundation behind miso soup, udon, soba, ramen, chawanmushi, nimono, and tamagoyaki.

Dashi has deep roots. Bonito was documented in Japanese cuisine as early as 757 CE, and kombu appeared around 839 CE. The term "dashi" itself came into common use during the Edo period (1603–1867). Centuries later, it remains the most indispensable stock in the Japanese kitchen.

At Tomato Japanese Grocery, we've spent over 20 years sharing authentic Japanese ingredients with our community, and we can tell you: nothing transforms a dish like homemade dashi. The reason is umami synergy. When kombu and bonito are combined, the resulting flavor is 7 to 8 times stronger than either ingredient alone. That's not marketing; that's science.

The Science of Umami: Why Kombu + Bonito Is Pure Magic

In 1908, Professor Kikunae Ikeda at Tokyo Imperial University made a breakthrough that changed how the world understands taste. While studying kombu dashi, he isolated glutamic acid and identified it as the source of a distinct savory flavor he called umami, the fifth basic taste alongside sweet, sour, salty, and bitter.

Five years later, his protégé Shintaro Kodama discovered that katsuobushi contains a different umami compound: inosinate (IMP). These two discoveries set the stage for something remarkable.

Research by Shizuko Yamaguchi at Japan's Institute of Taste and Food Preferences showed that when glutamic acid from kombu and inosinic acid from bonito are combined at a 1:1 ratio, the perceived umami intensity multiplies by 7 to 8 times. This synergy is the reason awase dashi tastes so much richer than the sum of its parts.

The world is catching on. The global umami flavors market was valued at roughly $5.1 billion in 2025 and is growing at a 7.3% annual rate. But the original, clean-label umami source has always been right here: scratch-made dashi. No additives, no MSG, just two natural ingredients working together.

What You Need: Ingredients and Sourcing Tips

For a standard 4-cup batch of awase dashi, you need:

• 10–15 grams of kombu (a piece roughly 4×4 inches)
• 15–20 grams of katsuobushi (about 2 loosely packed cups of shavings)
• 4 cups of soft water (filtered water works well in most US kitchens)

Choosing Your Kombu

Not all kombu is the same. Four main varieties are used for dashi, each with a distinct character:

• Hidaka kombu: Mild, versatile, and the easiest to find. Best for beginners.
• Rishiri kombu: Clean and delicate, favored in Kyoto-style cooking.
• Rausu kombu: Rich and bold, producing a deeper stock.
• Ma (True) kombu: Balanced flavor, considered the gold standard by many chefs.

If you're making dashi for the first time, start with Hidaka. It's forgiving and produces a reliably good stock.

What Quality Katsuobushi Looks Like

Good bonito flakes are thin, almost translucent, with a pale pink color and a clean smoky aroma. The production process behind katsuobushi is extraordinary: bonito fillets are boiled, smoked, dried, inoculated with mold, fermented, and sun-dried over weeks or months. It's one of the most complex fermented ingredients in all of Japanese cooking.

A Note on Kombu's White Powder

You may notice a white, powdery coating on your kombu. This is mannitol, a naturally occurring substance packed with umami compounds. Never wipe it off, rinse it, or scrub it away. It's flavor, not dirt.

Water Matters

Use soft water with a hardness level between 0 and 30. Hard water reacts with proteins in kombu and can produce a bitter, unpleasant taste. Most filtered tap water in the US falls within an acceptable range.

We stock multiple kombu varieties and premium katsuobushi at Tomato Japanese Grocery, both in our Marietta, GA store and through our online shop with nationwide shipping. If you're unsure which to pick, just ask. We're always happy to help.

Step-by-Step: How to Make Ichiban Dashi (First Dashi)

Ichiban dashi (一番だし) is the first extraction, and it produces the most delicate, aromatic stock. Here's how to make it right.

1. Prep the kombu. Gently wipe the surface with a damp cloth to remove any dust or grit. Do not rinse it under running water, and do not scrub off the white powder (mannitol). That powder is pure umami.
2. Cold soak. Place the kombu in a pot with 4 cups of cold, soft water. Let it soak for 20 to 30 minutes. This begins a gentle extraction of glutamic acid without any heat.
3. Heat slowly. Set the pot over medium-low heat. Watch carefully. You want to remove the kombu just before the water reaches a boil, ideally at 60–64°C (140–150°F). If you don't have a thermometer, look for small bubbles forming on the bottom and sides of the pot. Boiling the kombu releases bitter compounds and creates a slimy texture you don't want.
4. Add katsuobushi. Once the kombu is out, bring the water to a gentle simmer. Add the bonito flakes, then immediately turn off the heat. Let the katsuobushi steep for 3 to 4 minutes. The flakes will slowly sink to the bottom as they release their inosinic acid.
5. Strain carefully. Pour the stock through a fine-mesh strainer lined with cheesecloth or a clean kitchen towel. Do not squeeze the bonito flakes. Squeezing pushes out fine particles that make the dashi cloudy and can introduce a fishy off-note.

The result is ichiban dashi: golden, clear, and deeply aromatic. It's ideal for clear soups (suimono), chawanmushi, and miso soup, where the dashi's flavor takes center stage.

Cold-Brew Dashi (Mizudashi): The No-Heat Method

If you prefer a hands-off approach, mizudashi is your friend. Simply place a piece of kombu in a jar or pitcher of cold water, cover it, and refrigerate for 2 to 5 hours or overnight. The result is a cleaner, more delicate stock with less bitterness than the heated method.

You can make a kombu-only cold brew, or add katsuobushi alongside the kombu for a fuller flavor. Either way, there's no temperature to monitor and no pot to watch.

This method is perfect for meal prep. Drop your kombu in water on Sunday night and wake up Monday morning with ready-to-use dashi. For anyone new to making stock from scratch, mizudashi is a low-pressure way to start.

Don't Waste a Drop: Niban Dashi and Zero-Waste Uses

Your spent kombu and katsuobushi still have flavor to give. Niban dashi (二番だし) is the second extraction: place the used solids back in a pot with fresh water, bring it to a simmer, and cook for about 10 minutes. The resulting stock is lighter and milder, making it well suited for simmered dishes (nimono), dipping sauces, and braising liquids.

After that, the solids can still be put to work:

• Chop the spent kombu and simmer it with soy sauce and mirin to make tsukudani, a savory-sweet condiment for rice.
• Dry out the used katsuobushi in a pan, then blend it with sesame seeds and nori to create homemade furikake rice seasoning.
• Add both directly into your next pot of miso soup for extra body.

This zero-waste approach reflects a growing consumer shift toward clean labels and sustainability. Natural umami flavors are expected to account for 60% of the umami market as that shift accelerates. It also reflects something we believe in deeply at Tomato Japanese Grocery: respect for ingredients, from first use to last.

How to Use and Store Your Homemade Dashi

Storage is simple. Refrigerate dashi in an airtight container for up to 3 days. For longer storage, pour it into ice cube trays and freeze for up to 1 month. Frozen dashi cubes are incredibly convenient: just pop a few into a pot whenever you need them.

As for what to cook, the list is long:

• Miso soup (the classic first project)
• Udon, soba, and ramen broths
• Chawanmushi (savory egg custard)
• Tamagoyaki (Japanese rolled omelet)
• Nimono (simmered vegetables and proteins)
• Tempura dipping sauce
• Nikujaga, oyakodon, and other one-pot dishes
• Rice-cooking liquid for extra-flavorful steamed rice

Dashi also works beautifully outside Japanese cooking. Try it as a substitute for chicken or vegetable stock in risotto, pasta sauces, or braised meats. The umami depth it adds is remarkable, and it does so with far less sodium and fat than most commercial broths and bouillon cubes.

Start with miso soup. It's simple, satisfying, and the single best way to taste what your homemade dashi can do. From there, you'll find yourself reaching for it in dish after dish. That's how dashi becomes a gateway to Japanese pantry mastery.

Start Your Dashi Journey with Tomato Japanese Grocery

For over 20 years, our family has been passionate about bringing authentic Japanese ingredients to our community. We know from experience that the quality of your kombu and katsuobushi makes all the difference in your finished dashi. Sourcing matters.

You can shop with us in person at our store in Marietta, Georgia, or order online for nationwide delivery. We ship with eco-friendly packaging and handle every order with care, because these ingredients deserve it.

If you have questions about which kombu variety to try or what katsuobushi will work best for your cooking style, reach out. Our team is always happy to help.

Making dashi from scratch is a small act, but it connects you to centuries of Japanese culinary tradition. Two ingredients, a pot of water, and a few minutes of your time. That's all it takes to bring something truly special into your kitchen.