Passion fruit sour soup with tomatoes and tofu

Look at Thai and Chinese sour soup recipes and you'll see there's a whole spectrum of techniques for building acidity into a broth. Today's passion fruit sour soup draws on tart fruit, tomatoes, and lime to achieve that tanginess.

I'd wager if you asked a random sample of an average Anglo population what they knew of sour soups, many answers would be limited to "hot and sour," but this is a global category of soup. There's the Slavic sourdough soups such as Polish żurek, yoghurt soups like Turkish yayla çorbasi, Thai soups like tom som and tom yum, Vietnamese canh chua, Indian rasams, Ugandan malakwang, sopa de lima from The Yucatán, and countless others I don't remember or will never encounter because the list is so long.

China has its own tradition of sour soups, numerous in style and quantity, with regional variants galore. A discussion of sour soups in China is incomplete without a whiplash-inducing mega-nod toward Guizhou, with its tart fermented rice water and sour tomato soups, both of which have subclassifications that expand the category dramatically. There's also Sichuan suan cai yu, a lacto-fermented vegetable (napa cabbage in the North, mustard greens in the South) soup with a numbing Sichuan peppercorn base.

And finally (but not definitively), we can't ignore the sour soups of Yunnan, prepared with fruits, fermented bamboo, and other acidic ingredients. In my two visits to Dali, in Western Yunnan, I spent many hours using my phone to translate poster displays outside of restaurants. Passion fruit sour beef soup appeared repeatedly in the translations, but a vegan version proved elusive (the one vegan restaurant I found with it on the menu informed me they were no longer serving this dish). I added it to my travel notes to come back to later and moved on.

Ingredients and variations

Well, "later" finally arrived, and with a peak summer garden full of tomatoes as a bonus. I looked to Rednote/Xiaohongshu, the popular Chinese social media platform, for an idea of ingredients and quantities. The basics became clear: fry aromatics as a base; layer with tomatoes and passionfruit; season with soy, vegan oyster sauce, sugar, and salt; then brighten it all up with lime and fresh herbs to serve.

All in all it takes about an hour to prepare. Much of that time is dedicated to readying the tofu, which I boil in salted water and then lightly fry to make it extra sturdy. You can skip this step if you're short on time and add tofu directly to the pot, but if you do then use a firm tofu that can hold up in a liquid dish. You can also just follow the boiling step but skip the frying if you want a softer tofu that still holds up well in a soup.

Vegan oyster sauce is readily available at Chinese grocers. In the UK, Lee Kum Kee is the market leader and they sell two vegan options. First is their newer vegan oyster flavour sauce, which has a distinctive seafood-y taste. Second is their classic mushroom based vegetarian stir fry sauce. Both can be used as a 1:1 for nonvegan oyster sauce in any recipe. It's a handy condiment for stir fries, so it's worth keeping a bottle around.

Passionfruit and tomato sour soup with tofu

The perfect soup for hot weather or whenever your appetite is low, this Yunnan style sour soup is best served with a bowl of hot steamed rice. The passion fruit and tomatoes you use may be more or less acidic than mine, so adjust with sugar and lime to suit your palate.

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Prep Time 15 minutes mins

Cook Time 1 hour hr

Servings: 3 people, with rice

Cuisine: Chinese

Ingredients Method

Ingredients

  

The tofu

• 400 grams medium firm tofu
• 600 millilitres water
• 12 grams salt 2 teaspoons
• oil, for frying

The soup

• 2 tablespoon vegetable oil
• 80 grams finely minced onion packed ½ cup plus 2 tablespoons
• 10 grams minced garlic 1 packed tablespoon
• 10 grams minced ginger 2 packed teaspoons
• chopped fresh chillies optional
• 200 grams roughly chopped tomatoes
• 400 millilitres water
• 3 passion fruits, pulped approximately 90 grams pulp, or a scant ⅓ cup
• 2 tablespoons light soy sauce
• 1 tablespoon vegan oyster or mushroom sauce
• 1 tablespoon sugar
• ¼ teaspoon salt
• 1-2 teaspoons lime juice
• Fresh coriander and spring onion
• thin slices of lime optional

Method

 

Prepare the tofu

1. Slice the tofu into thin ½ centimetre (just shy of ¼ inch) pieces. The length and width is up to you. Pop the slices in a saucepan and add the water and salt. Heat on high until it boils, and then turn it down to a simmer. Cook for 5 minutes and then turn off the heat. Leave the tofu in the salt water for a further 10 minutes.
2. Drain the tofu and lay a tea towel out. Lay the steamy sliced tofu on the tea towel in one layer. Try to keep each piece separate because hot plain tofu sticks to each other. Leave to cool for 10-15 minutes.
3. Drizzle a little oil (you don't need much) in a nonstick frying pan and fry the tofu on both sides until you see some light colouring. You're not aiming for a crispy fried skin. Pop the fried tofu on a plate while you make the soup.
   

Make the sour soup

1. You can use the same skillet for making the soup. Heat the oil to medium and fry the onion, garlic and ginger for 8-10 minutes, or until lightly golden. Make sure you stir it semi regularly to avoid burning.
2. Add the tomatoes and cook for around 5 minutes or until broken down. Then add water, passion fruit pulp, soy sauce, vegan oyster or mushroom sauce, sugar, and salt. Slide in the tofu and simmer for another 10-15 minutes.
3. Add a teaspoon of the lime juice and give the broth a taste. It should be a balance of salty and sour with a little bit of sweetness. Add the additional teaspoon of lime juice if you want more sourness.
4. Dish up and garnish with spring onion, coriander, and sliced limes, if using. Serve with steamed rice.