Japanese Seaweed Soup: A Simple Wakame and Tofu Recipe

Japanese seaweed soup is a light miso soup made with rehydrated wakame, tofu, and savory dashi; it is commonly served warm as part of a Japanese meal. This version uses kombu for a gentle, vegetarian broth, and the quick-cooking ingredients keep the seaweed tender rather than mushy.

Ingredients

4.5 cups (1.06 L) cold water
1 piece dried kombu, about 4 inches square (10 cm square; about 5 g)
2 tablespoons (4 g) dried wakame
7 ounces (200 g) soft or silken tofu, cut into small cubes
3 tablespoons (54 g) white miso or awase miso
2 medium scallions (about 20 g), thinly sliced
1 teaspoon (5 ml) soy sauce, optional, for a slightly saltier finish

Instructions

Steep the kombu. Wipe any visible grit from the kombu with a damp cloth, but do not scrub off its pale surface coating. Put the kombu and cold water in a saucepan and leave them to steep for 20 minutes. This short soak begins extracting flavor before the water heats, giving the broth a rounded savory taste without needing a long simmer.
Rehydrate the wakame and prepare the garnishes. Lift the kombu out of the water and set it aside. Put the dried wakame in a small bowl, cover it with cool water, and soak for 5 minutes, or according to the package if it gives a different time. While it soaks, cut the tofu into roughly 1/2-inch (1-cm) cubes and slice the scallions. Drain the wakame well; if the pieces are very long, cut them into bite-size lengths. It will expand substantially as it takes up water.
Make the kombu dashi. Set the saucepan over medium-low heat and warm the kombu soaking water for about 10 minutes, watching for small bubbles to gather around the edge. Remove the kombu just before the liquid reaches a full boil. Avoid boiling the kombu: prolonged boiling can make the broth cloudy or give it a slippery texture. You now have a mild kombu dashi. Discard the kombu or save it for another use, such as adding to a simmered dish.
Warm the tofu. Add the cubed tofu to the dashi and cook gently for 3 minutes. Keep the liquid at a quiet simmer rather than letting it boil hard; vigorous bubbling can break delicate tofu into small pieces. Stir once, slowly, if needed, and take care not to press the cubes against the side of the pan.
Add the wakame. Stir in the drained wakame and heat for 1 minute, just until it is hot and soft. Dried wakame is already thin and cooks quickly after rehydrating, so it does not need to simmer for a long time. If your seaweed is a thicker variety, follow the package directions and give it the extra time it needs to become tender.
Dissolve the miso off the heat. Turn off the burner. Ladle about 1/2 cup (120 ml) of hot broth into a small bowl, add the miso, and stir until smooth. Pour this mixture back into the saucepan and stir gently. Taste before adding the optional soy sauce, since miso and some dashi products can already be salty. Serve promptly, topped with sliced scallions.

Tips

Keep miso out of a rolling boil. High heat can dull its delicate aroma and make the finished soup less fragrant. Dissolving it after turning off the heat is easy and helps the broth taste clean. If the soup cools before serving, warm it gently without bringing it to a boil.
Check the wakame before measuring. The recipe quantity is for dried seaweed, not rehydrated seaweed. If you only have prepared, hydrated wakame, use about 1/2 cup (25 g), drain it well, and add it at the end just long enough to warm through. The exact weight can vary by cut and how thoroughly it was drained.
Choose the dashi that suits your table. Kombu dashi keeps this recipe vegetarian and has a light, sea-sweet flavor. For a more traditionally savory, fuller broth, replace the kombu dashi with 4 cups (960 ml) prepared bonito-and-kombu dashi; that version contains fish. Instant dashi granules are also convenient, but check the label because many include bonito and salt.
Season at the end. Miso varies in saltiness, and the broth reduces slightly as it heats. Taste after the miso is mixed in, then add soy sauce a few drops at a time only if it needs more seasoning. Adding salt or soy sauce early can make it difficult to balance the finished bowl.

Serving Suggestions

Serve the soup hot in small bowls, with a few scallion slices scattered over each portion. It works as a first course or as one part of a Japanese-style meal alongside steamed rice, grilled fish, tamagoyaki, or vegetables dressed with sesame. For a simple lunch, pair it with a rice bowl and a small plate of pickles. Since the broth is light, it complements richer or more strongly seasoned dishes without competing with them.

For the best texture, ladle the tofu and wakame evenly among the bowls before pouring in the broth. If serving several dishes, bring the soup to the table soon after adding the miso so the seaweed stays tender and the broth remains pleasantly aromatic. A small bowl is a useful portion: miso soup is commonly served alongside food rather than treated as a large, stand-alone entrée.

Variations

Use another seaweed. Dried wakame is the easiest choice because it rehydrates quickly and has a soft, pleasantly chewy texture. If you have fresh or salted wakame, rinse or soak it as directed on its package and adjust the amount to taste. Nori can be torn into the soup just before serving, but it softens quickly and makes the broth less clear; it is a different texture rather than a direct substitute for wakame.

Change the miso. White miso is mild and slightly sweet, while awase (blended) miso gives a deeper, more savory flavor. Red miso can also be used, but it is usually more assertive and often saltier, so begin with 2 tablespoons (36 g), taste, and add more if needed. Miso types vary by maker, so the amount is a starting point rather than a fixed rule.

Add vegetables or mushrooms. Thinly sliced mushrooms, daikon, or napa cabbage can make the soup more substantial. Add firm vegetables to the dashi early enough to become tender, then add tofu and wakame near the end. A handful of enoki or sliced shiitake can be added with the tofu; allow thicker mushroom slices a few extra minutes to soften before stirring in the miso.

Make a fish-based broth. Kombu-and-bonito dashi is a common alternative when a vegetarian broth is not needed. Prepare it according to the package or use a prepared stock, then continue with the tofu, wakame, and miso steps. Keep in mind that the flavor will be more pronounced, and that instant stock may already contain salt, so taste before adding soy sauce.

Storage and Reheating

For the best texture, make only as much as you plan to eat: wakame continues to soften while it sits in hot broth. If you have leftovers, refrigerate them within 2 hours in a covered container. Cooked soup keeps for 3–4 days in the refrigerator. The tofu may become a little firmer and the seaweed softer, but the soup is still usable if it has been handled and chilled promptly.

Reheat only the amount you need in a small saucepan over low to medium-low heat, stirring gently, until steaming hot. Avoid a hard boil, especially after miso has been added. If you are reheating leftovers, USDA guidance is to bring them to 165°F (74°C); check the soup with a food thermometer and then serve promptly. For the best flavor, you can also store plain kombu dashi separately from the tofu and wakame, then add fresh ingredients and miso when you reheat it. Freeze leftovers in a freezer-safe container for up to 2 months, though the tofu can turn more porous and the wakame softer after thawing.

Frequently Asked Questions

Is Japanese seaweed soup the same as miso soup?
Wakame seaweed soup is a common kind of miso soup, but miso soup is a broader category. It can be made with different dashi, vegetables, tofu, or other additions, and many versions do not include seaweed. This recipe combines wakame and tofu with kombu dashi and miso.

Can I use nori instead of dried wakame?
You can, but the result will be different. Nori becomes soft very quickly and can cloud the broth, while wakame keeps more of its slippery, tender bite. Tear a small sheet of nori into pieces and add it right before serving rather than soaking it like dried wakame.

Can I make this soup vegetarian or vegan?
Yes. Use the kombu dashi in this recipe and check that the miso contains no fish-based ingredients; most plain miso is plant-based, but labels are worth checking. Avoid bonito dashi and instant stock containing fish. The listed tofu version is vegan if the chosen miso and any optional seasonings are also plant-based.

Why is my soup too salty?
Miso brands and dashi powders differ in salt content, and a concentrated stock can make the bowl taste overly seasoned. Add miso gradually, taste before using the optional soy sauce, and dilute a salty pot with a little hot water or unsalted kombu dashi. If you use instant dashi, follow its package quantity rather than making it extra strong.

Can I prepare the soup ahead?
You can make the kombu dashi ahead and refrigerate it, covered, for up to 3–4 days. For the freshest texture, store the broth separately and add tofu, wakame, and miso shortly before serving. If the soup is already assembled, refrigerate it within 2 hours and reheat gently, knowing that the seaweed will be softer than when freshly made.

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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes

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