Vegan Soba Noodle Soup (Sansai Soba)

May 5, 2020

This soba noodle soup features fresh spring veggies, crispy tofu, bamboo shoots, and mushrooms in a smoky, savory broth with toothy buckwheat noodles. It’s both refreshing and hearty – a slurpable and soothing one-bowl meal.

Soba Noodle Soup Goes Green 

If you’ve followed me for any amount of time, you might have noticed that I share a lot of noodle soups. From ramen to udon to nabe hot pot, steamy soup with chewy noodles makes a really satisfying meal.

I also really enjoy meals that use an abundance of fresh green veggies – from green smoothies to pasta primavera. The wealth of nutrients the veggies bring, combined with the vibrant shades of color, are a mood and energy booster.

It only makes sense that I’d combine these approaches and make a noodle soup that’s overflowing with green veggies. In honor of spring and its seasonal harvest, I put together this soba noodle soup, also known as sansai soba.

A hot steamy bowl of vegan soba noodle soup with veggies

The Inspiration for This Soba Noodle Soup

This dish was inspired by one of my favorite noodle shops in the city, a soba restaurant called Cocoron. They have a vegan sansai soba, which uses their excellent house-made buckwheat noodles, a rich plant-based broth, and a veggie mix called “sansai”. If you ever visit New York, do pay them a visit.

(If you live in New York, please consider ordering takeout or frozen items from them to support them during these difficult times.)

Spending 99% of my time at home lately, I wanted to recreate their sansai soba, not just so I could enjoy it myself, but so you can experience it at home as well, wherever you may be.

So How do You Make This?

There are a few components here, all of them pretty simple, but I’ll walk you through them.

Soba Noodles

If you’re not familiar with soba, they’re noodles made at least partially with buckwheat. They have a light brown color and a chewy texture with grainy bits here and there. They taste like other wheat noodles, but with a very faint sourness.

They are less refined and more nutritious than most wheat noodles. Some (but not all) are made from 100% buckwheat – that kind is gluten-free.

Outside Japan, soba most frequently come dried, but if you are lucky, you can find fresh soba made by Sun Noodle.

Close-up photo of vegan Japanese soba noodle soup

Plant-Based Soba Tsuyu (Broth)

I used a simple vegan broth (also known as tsuyu) for this dish. Similar to dashi, the main flavor comes from dried shiitake mushrooms, two types of seaweed, and soy sauce, which combine for a fragrant, savory, earthy soup.

For some extra nuance, I added a bit of sake (this is optional), which adds a sweet aroma and enhances the other flavors. Liquid smoke adds a touch of woody smokiness and maple syrup a subtle sweetness.


Sansai is a Japanese term that refers to a mixture of vegetables and mushrooms, which were traditionally foraged. There are lots of greens and shoots and things that look wild and nourishing.

Japanese sansai mixed vegetables, bamboo shoots, and mushrooms

Fiddlehead ferns, bamboo shoots, wood ear mushrooms, and enoki mushrooms are common sansai ingredients.

It is possible to buy sansai in a Japanese grocery store, but you don’t need to buy sansai to make this recipe! More on this below.

Fresh Veggies and Mushrooms

Since it’s spring, I couldn’t resist adding asparagus and broccolini. I included spinach and shimeji mushrooms to round it out.

To cook the veggies and mushrooms, I blanched them in a pot of boiling water very briefly to preserve the color and flavor.

Crispy Tofu

Since everything else in the soup is boiled or blanched, I wanted to include something dry and crispy in the soup.  I baked aburaage (fried tofu) until crispy and it makes a perfect complement.

If you can’t find aburaage, feel free to use cubes of firm tofu instead.

Two bowls of vegan sansai soba noodle soup with fresh spring vegetables

What to do if You Don’t Have Sansai

You can replace the sansai with any combination of the following:

  • More of the asparagus, spinach, mushrooms, or broccolini already in the recipe
  • Other fresh veggies not in the recipe – snow peas, green beans, kale, bok choy, etc (you’ll want to blanch these until just cooked)
  • Canned bamboo shoots and/or water chestnuts
  • Rehydrated, sliced, and blanched wood ear mushrooms
  • Any kind of mushrooms you feel like (blanch these as well)

Cooking Workflow

It’s helpful to get set up before you start cooking, to make things easier. I recommend a two-pot setup here:

  • You’ll simmer the broth in one pot – it takes at least 30 minutes to infuse the flavors of the mushrooms and seaweed. This pot won’t require too much attention as it simmers, but it will need to be drained.
  • You’ll boil water in another pot and use this to boil the noodles and each of the fresh veggies and mushrooms. It’s important to pay close attention to this pot, since the boiling time can be different for each ingredient. You want the noodles properly chewy and none of the veggies overcooked.
Pulling soba soba buckwheat noodles from a bowl of vegan soup with chopsticks

Final Thoughts

This is a pretty long post about a fairly simple dish. My hope is that you’ll be able to use this guide to make a soothing bowl of soba noodle soup for yourself and those you care about with a flexible variety of different ingredients.

Confused? Have questions? Leave a note below and I’ll help you out.

Looking for Zaru Soba – the cold dipping noodles? Find the recipe here.

Plant-Based Sides to Accompany Your Soba

More Plant-Based Japanese-Inspired Noodles

  • Yaki Udon – fat, toothy noodles cooked in a savory sauce with veggies and mushrooms
  • Tonkotsu Ramen – ramen in a brilliantly creamy, intensely nutty and aromatic broth
  • Tsukemen (Dipping Ramen) – you dip the ramen noodles into a rich, concentrated broth and slurp them down
Soba buckwheat noodles in vegan tsuyu broth with green spring vegetables


Vegan Soba Noodle Soup (Sansai Soba)

This soba noodle soup features fresh spring veggies, crispy tofu, bamboo shoots, and mushrooms in a smoky, savory broth with toothy buckwheat noodles. It’s both refreshing and hearty – a slurpable and soothing one-bowl meal.
Course Dinner
Prep Time 10 minutes
Cook Time 45 minutes
Servings 2
Author Thomas


  • 2 servings soba noodles dried or fresh
  • 1 cup sansai optional (see note)
  • 2 sheets aburaage cut into slices (or substitute 1 cup cubed tofu)

Veggies and mushrooms to blanch

  • 1 cup chopped asparagus
  • 1 cup chopped broccolini
  • 1 cup chopped spinach
  • 1 cup shimeiji mushrooms or enoki or other mushrooms


  • 1/2 cup sake
  • 6 cups water
  • 1/4 teaspoon liquid smoke
  • 3 dried shiitake mushrooms sliced
  • 1 piece kombu seaweed 2×2 inches or 5×5 centimeters
  • 1/2 sheet sushi nori seaweed 8×4 inches or 20×10 centimeters
  • 4 large coin-sized slices of ginger
  • 1 teaspoon maple syrup
  • 4 Tablespoons soy sauce

Optional garnishes

  • Radish sprouts
  • Green onions sliced thinly
  • Shichimi Togarashi


  • If using aburaage, preheat the oven to 400 degrees F or 205 degrees C.
  • Prepare two pots on the stove – one medium-sized one (2.5 quarts or 2.3 liters) for the broth and a large one (5 quarts or 4.7 liters) to cook the noodles and blanch the vegetables and mushrooms.
  • Fill the large pot 2/3 of the way with water and heat it over high heat.

Simmer the Broth

  • Combine all the Broth ingredients in the medium-sized pot, except for the maple syrup and soy sauce (you’ll add those two at the end). Bring the mixture to a simmer over medium heat, then reduce to medium-low heat. Simmer for at least 30 minutes to infuse the flavors.

Bake the Aburaage

  • Once the oven is preheated, place the sliced aburaage onto a baking sheet and bake for 10 minutes, or until crispy.

Boil the noodles and vegetables

  • Meanwhile, when the large pot of water reaches a boil, boil the noodles according to the instructions. You can even undercook them slightly, since they will continue to absorb liquid and soften one they’re combined with the broth. Remove the noodles, strain them, and rinse them with cool tap water to stop the cooking.
  • If you’re using cubed tofu (not aburaage), blanch the tofu cubes for 1 minute.
  • Cook the vegetables and mushrooms individually in the large pot. The asparagus, broccolini, and mushrooms need 30-45 seconds and the spinach needs about 10 seconds. Pay attention to the color of the vegetables – you want them to stay bright green for the best flavor and texture. Remove each vegetable from the pot, strain it, and rinse it with cool tap water.
  • You can blanch the sansai for 10 seconds to heat it up, but it’s already cooked, so this step is optional.

Strain and Season the Broth

  • By now, the broth should be well-infused. Strain out as much of the solids as possible. The nori will have disintegrated, so use a fine mesh strainer or cheesecloth to remove as much as you can.
  • Stir the soy sauce and maple syrup into the broth.

Combine, garnish, and serve

  • Divide the noodles, vegetables, and mushrooms evenly into two large bowls. Spoon broth over top of them until the bowl is nearly full. Add the crispy aburaage. Garnish with radish sprouts, green onions, or shichimi togarashi, as desired. Serve immediately.


If you don’t have sansai, you can increase the amounts of the other vegetables and mushrooms by 1/4 cup each.

The post Vegan Soba Noodle Soup (Sansai Soba) appeared first on Gastroplant.

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