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Okinawan Purple Sweet Potato & Bitter Melon Miso Soup

Name: Okinawan Purple Sweet Potato & Bitter Melon Miso Soup
Cuisine: okinawan
Ingredients: 0.7 oz dried kombu (kelp), wiped clean, cut into 5 cm strips; 6 1/4 cups filtered water, cold; 14 oz purple sweet potatoes (Okinawan variety), scrubbed, unpeeled, cut into 2 cm cubes; 7 oz bitter melon (goya), halved, seeded, sliced into 0.5 cm half-moons; 5.3 oz carrots, peeled, cut into 1 cm half-moons; 3.5 oz shiitake mushrooms, stems removed, caps sliced; 2 oz wakame seaweed, rehydrated in cold water for 10 min, drained; 1/4 cup white shiro miso paste, kept separate until serving; 1 tbsp extra-virgin olive oil, cold-pressed, high polyphenol; 1 tbsp fresh shiso leaves, thinly sliced

A vibrant, earthy broth featuring the signature purple flesh of Okinawan sweet potatoes and the distinct, bite of bitter melon.

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Okinawan Purple Sweet Potato & Bitter Melon Miso Soup — authentic Okinawan recipe from Taste Meridian

Ingredients

Base & Aromatics

0.7 ozdried kombu (kelp), wiped clean, cut into 5 cm strips
6 1/4 cupsfiltered water, cold

Vegetables

14 ozpurple sweet potatoes (Okinawan variety), scrubbed, unpeeled, cut into 2 cm cubes
7 ozbitter melon (goya), halved, seeded, sliced into 0.5 cm half-moons
5.3 ozcarrots, peeled, cut into 1 cm half-moons
3.5 ozshiitake mushrooms, stems removed, caps sliced
2 ozwakame seaweed, rehydrated in cold water for 10 min, drained

Seasoning

1/4 cupwhite shiro miso paste, kept separate until serving
1 tbspextra-virgin olive oil, cold-pressed, high polyphenol

Garnish

1 tbspfresh shiso leaves, thinly sliced

Equipment

heavy-bottomed Dutch oven or large soup pot — ensures even heat distribution to prevent scorching the sweet potatoes and allows for gentle simmering
fine-mesh sieve or ladle with small holes — essential for dissolving miso without overcooking it or leaving clumps

A little context

Rooted in the Okinawan 'Goya Champuru' and 'Nimono' traditions, this soup strips away the traditional addition of sugar and seed oils (like canola) often found in modern adaptations. We honor the 'hara hachi bu' (eat until 80% full) philosophy by focusing on high-volume, low-calorie, high-nutrient density ingredients. The sweetness is derived solely from the natural caramelization of the purple sweet potatoes, respecting the ingredient's integrity rather than masking its flavor with refined sweeteners.

Method

01
Prepare the Dashi Base
In a large pot, combine the filtered water and dried kombu strips. Bring to a bare simmer over medium heat. Just before boiling (small bubbles forming at the edges), remove the pot from heat and take out the kombu. Do not boil the kombu, or the broth will become slimy and bitter. This creates a mineral-rich dashi base.
02
Blanch the Bitter Melon
While the water heats, place the sliced bitter melon in a bowl, toss with 1 tsp of coarse sea salt, and let sit for 10 minutes. Rinse thoroughly under cold water to remove excess salt and bitterness.
03
Simmer the Root Vegetables
Return the pot with the dashi to medium heat. Add the purple sweet potato cubes and carrots. Bring to a gentle simmer and cook for 15 minutes, or until the sweet potatoes are tender but not falling apart. The purple color should begin to leach slightly, turning the broth a soft violet.
04
Add Mushrooms and Melon
Add the shiitake mushrooms and the blanched bitter melon to the pot. Continue to simmer for another 10 minutes until the bitter melon is tender-crisp. Overcooking bitter melon makes the texture unpleasant.
05
Finish with Wakame
Stir in the rehydrated wakame seaweed. Cook for just 2 minutes; wakame expands quickly and can become slimy if boiled too long.
06
Dissolve the Miso
Turn the heat to the lowest setting. Ladle about 1/2 cup of the hot broth into a small bowl and whisk in the white miso paste until completely smooth. Pour the dissolved miso mixture back into the main pot. Do not boil the soup after adding miso.
07
Temper with Olive Oil
Remove the pot from the heat entirely. Drizzle the extra-virgin olive oil over the soup and stir gently. This adds a layer of monounsaturated fats.
08
Serve Immediately
Ladle into pre-warmed bowls. Garnish with fresh sliced shiso leaves if using. Serve hot, ideally with a side of plain brown rice or a small portion of fermented vegetables.

Pro tips

✦When selecting purple sweet potatoes, look for firm tubers with smooth skin and no soft spots; the flesh should be a deep, vibrant violet.
✦Never boil the miso after adding it.
✦If the bitter melon is too bitter for your palate, salt it for 15 minutes instead of 10, rinse well, and squeeze out excess water before cooking.
✦For a deeper umami hit, soak the shiitake stems in the water while making the dashi, then remove them before adding the vegetables.

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Equipment

Dutch Oven →

Specialty ingredients

Kombu →Miso →Shiso →

Substitutions

purple sweet potatoes → orange sweet potatoes or white yams (will reduce anthocyanin intake but maintains the texture and sweetness profile)
white shiro miso → red aka miso (use less (start with 40g) as red miso is saltier and more pungent; adds more depth but less sweetness)
bitter melon → zucchini or chayote (best to stick with the original)

Storage

Cool completely and store in a glass container in the refrigerator for up to 3 days. The flavor of the miso and vegetables deepens overnight. Do not freeze with the miso already dissolved, as the texture may separate; freeze the broth and vegetables separately, then add fresh miso upon reheating.

What to serve with it

Hot green tea (sencha) to complement the earthy notes
Sparkling water with a wedge of yuzu or lemon
A small side of fresh natto or pickled daikon radish
Steamed brown rice or quinoa for a complete meal

FAQ

Why is the soup violet/purple?+

The color comes from the anthocyanins in the purple sweet potatoes.

Can I make this broth ahead of time?+

Yes, you can make the dashi base and chop vegetables 2 days in advance.

Is this soup gluten-free?+

Yes, provided you use a certified gluten-free miso (some traditional misos use barley or wheat) and ensure your kombu and seaweed are processed in a gluten-free facility.